A good IT administrator secure his network behind firewalls. An sensible spot in security is USB storage device. To prevent users from connecting to USB storage devices, use one or more of the following procedures, as appropriate for your situation. When you have already instaled USB device you need to deny access on it. You can do this directly from registry settings. We strongly recommended that you back up the registry before making any changes and that you only change values in the registry that you understand or have been instructed to change.Enable USB Storage devices
Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\USBSTOR] "Start"=dword:00000003 "Type"=dword:00000001 "ErrorControl"=dword:00000001 "ImagePath"=hex(2):5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,\ 74,00,5c,00,73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,44,00,52,\ 00,49,00,56,00,45,00,52,00,53,00,5c,00,55,00,53,00,42,00,53,00,54,00,4f,00,\ 52,00,2e,00,53,00,59,00,53,00,00,00 "DisplayName"="USB Mass Storage Driver" "DriverPackageId"="v_mscdsc.inf_x86_neutral_ef3a0c30c03f0225" "BootFlags"=dword:00000004 Disable USB Storage devices Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\USBSTOR] "Start"=dword:00000004 "Type"=dword:00000001 "ErrorControl"=dword:00000001 "ImagePath"=hex(2):5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,\ 74,00,5c,00,73,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,44,00,52,\ 00,49,00,56,00,45,00,52,00,53,00,5c,00,55,00,53,00,42,00,53,00,54,00,4f,00,\ 52,00,2e,00,53,00,59,00,53,00,00,00 "DisplayName"="USB Mass Storage Driver" "DriverPackageId"="v_mscdsc.inf_x86_neutral_ef3a0c30c03f0225" "BootFlags"=dword:00000004
Wednesday, September 9, 2009
How you can prevent users from connecting to a USB storage device
Wednesday, July 1, 2009
HTML - button and css file
Create an dynamic button in html
______You need to download button file. this contain a .png file and a .psd file. You can use this button, like is showed in code example.
______You need to download button file. this contain a .png file and a .psd file. You can use this button, like is showed in code example.
Tuesday, June 30, 2009
CISCO Routers Commands
Commands in User Exec Mod:
| Commands | Explication | |
| enable | Turn on privileged commands | |
| exit | Exit from the EXEC | |
| logout | Exit from the EXEC | |
| ping | Send echo messages | |
| show | Showrunning system information | |
| access-lists | List access lists | |
| arp | Arp table | |
| cdp | CDP information | |
| clock | Display the system clock | |
| controllers | Interface controllers status | |
| frame-relay | Frame-Relay information | |
| history | Display the session command history | |
| interfaces | Interface status and configuration | |
| ip | IP information | |
| running-config | Current operating configuration | |
| startup-config | Contents of startup configuration | |
| version | System hardware and software status | |
| traceroute | Trace route to destination | |
Commands in Global Config Mod:
| Commands | Explication |
| access-list | Add an access list entry |
| cdp | Global CDP configuration subcommands |
| enable | Modify enable password parameters |
| end | Exit from configure mode |
| exit | Exit from configure mode |
| hostname | Set system's network name |
| interface | Select an interface to configure |
| ip | Global IP configuration subcommands |
| line | Configure a terminal line |
| no | Negate a command or set its defaults |
| router | Enable a routing process |
| username | Establish User Name Authentication |
Commands in Priviledged Exec Mod:
| Commands | Explication | |
| clear | Reset functions | |
| configure | Enter configuration mode | |
| copy | Copy from one file to another | |
| debug | Debugging functions (see also 'undebug') | |
| disable | Turn off privileged commands | |
| enable | Turn on privileged commands | |
| erase | Erase a filesystem | |
| exit | Exit from the EXEC | |
| logout | Exit from the EXEC | |
| no | Disable debugging informations | |
| ping | Send echo messages | |
| reload | Halt and perform a cold restart | |
| show | Show running system information | |
| access-lists | List access lists | |
| arp | Arp table | |
| cdp | CDP information | |
| clock | Display the system clock | |
| controllers | Interface controllers status | |
| frame-relay | Frame-Relay information | |
| history | Display the session command history | |
| interfaces | Interface status and configuration | |
| ip | IP information | |
| running-config | Current operating configuration | |
| startup-config | Contents of startup configuration | |
| version | System hardware and software status | |
| traceroute | Trace route to destination | |
| undebug | Disable debugging functions (see also 'debug') | |
| write | Write running configuration to memory, network, or terminal | |
Sunday, June 21, 2009
About radar - radiolocation
History of radar
_____Nobody can be credited with "inventing" RADAR. The idea had been around for a long time - a spotlight that could cut through fog. But the problem was that it was too advanced for the technology of the time. It wasn't until the early 20th century that a radar system was first built. One of the biggest advocators of radar technology was Robert Watson-Watt, a British scientist.
_____In 1887 the German physicist Heinrich Hertz began experimenting with radio waves in his laboratory. He found that radio waves could be transmitted through different types of materials, and were reflected by others, such as conductors and dielectrics. The existence of electromagnetic waves was predicted earlier by the Scottish physicist James Clerk Maxwell, but it was Hertz who first succeeded in generating and detecting radio waves.
_____The history of radar began in the 1900s when engineers invented simple uni-directional ranging devices. While radar development was pushed because of wartime concerns, the idea first came about as an anti-collision system. After the Titanic ran into an iceberg and sank in 1912, people were interested in ways to make such happenings avoidable. The technique developed through the 1920s and 1930s, leading to the introduction of the first early warning radar networks just before the opening of World War II. Progress during the war was rapid; by the end the United States widely deployed radars that fit in a single semi-trailer.
_____The place of radar in the larger story of science and technology is argued differently by different authors. Radar, far more than the atomic bomb, contributed to Allied victory in World War II. Robert Buderi states that it was also the precursor of much modern technology.
_____Great Britain made a big effort to develop radar in the years leading up to World War Two. Some people credit them with being pioneers in the field. As it was, the early warning radar system, called "Chain Home", that they built around the British Isles warned them of all aerial invasions. This gave the outnumbered Royal Air Force the edge they needed to defeat the German Luftwaffe during the Battle of Britain.
_____Although radar was originally introduced to give warning of the approach of hostile aircraft it has since been further developed to do much more than its original task. Modern radar equipment plays a vital part in all the operational roles of the RAF: as an aid to accurate bombing; in airborne detection and interception equipment; for the control of guided weapons; as navigational and landing aids; in cloud and collision warning devices. It has many other uses in the civilian as well as in the Service field.
_____Radar is a method of using radio waves to detect the existence of an object and then to find its position in relation to a known point, usually the site of the radar installation.
By means of radar the presence of moving or stationary objects such as aircraft, ships, and landmasses can be detected. In addition, information concerning the exact position of the object (usually referred to as the 'target') and its speed and course, where applicable, can be obtained. The word 'radar' is coined from the initial letters of the phrase: RAdio Detection And Ranging.
_____Radar has been the root of a wide range of achievements since the war, producing a veritable family tree of modern technologies. Because of radar, astronomers can map the contours of far-off planets, physicians can see images of internal organs, meteorologists can measure rain falling in distant places, air travel is hundreds of times safer than travel by road, long-distance telephone calls are cheaper than postage.
2. Principles of radiolocation
_____2.1. General principles of radiolocation
_____Radiolocating is the process of finding the location of something through the use of radio waves. It generally refers to passive uses, particularly radar — as well as detecting buried cables, water mains, and other public utilities. It is similar to radio navigation, but radiolocation usually refers to passively finding a distant object rather than actively one's own position. Both are types of radio determination. Radiolocation is also used in Real Time Locating Systems (RTLS) for tracking valuable assets.
_____Conventional radar systems comprise a collocated transmitter and receiver, which usually share a common antenna to transmit and receive. A pulsed signal is transmitted and the time taken for the pulse to travel to the object and back allows the range of the object to be determined.
_____In a passive radar system, there is no dedicated transmitter. Instead, the receiver uses third-party transmitters in the environment, and measures the time difference of arrival between the signal arriving directly from the transmitter and the signal arriving via reflection from the object. This allows the bistatic range of the object to be determined. In addition to bistatic range, a passive radar will typically also measure the bistatic Doppler shift of the echo and also its direction of arrival. These allow the location, heading and speed of the object to be calculated. In some cases, multiple transmitters and/or receivers can be employed to make several independent measurements of bistatic range, Doppler and bearing and hence significantly improve the final track accuracy.
_____The radar antenna, transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to antenna which is usually located at the same site as the transmitter. The time it takes for the reflected waves to return to the dish enables a computer to calculate how far away the object is, its radial velocity and other characteristics.
_____Electromagnetic waves reflect from any large change in the dielectric or diamagnetic constants. This means that a solid object in air or a vacuum, or other significant change in atomic density between the object and what is surrounding it, will usually scatter radar (radio) waves. This is particularly true for electrically conductive materials, such as metal and carbon fiber, making radar particularly well suited to the detection of aircraft and ships.
_____Nobody can be credited with "inventing" RADAR. The idea had been around for a long time - a spotlight that could cut through fog. But the problem was that it was too advanced for the technology of the time. It wasn't until the early 20th century that a radar system was first built. One of the biggest advocators of radar technology was Robert Watson-Watt, a British scientist.
_____In 1887 the German physicist Heinrich Hertz began experimenting with radio waves in his laboratory. He found that radio waves could be transmitted through different types of materials, and were reflected by others, such as conductors and dielectrics. The existence of electromagnetic waves was predicted earlier by the Scottish physicist James Clerk Maxwell, but it was Hertz who first succeeded in generating and detecting radio waves.
_____The history of radar began in the 1900s when engineers invented simple uni-directional ranging devices. While radar development was pushed because of wartime concerns, the idea first came about as an anti-collision system. After the Titanic ran into an iceberg and sank in 1912, people were interested in ways to make such happenings avoidable. The technique developed through the 1920s and 1930s, leading to the introduction of the first early warning radar networks just before the opening of World War II. Progress during the war was rapid; by the end the United States widely deployed radars that fit in a single semi-trailer.
_____The place of radar in the larger story of science and technology is argued differently by different authors. Radar, far more than the atomic bomb, contributed to Allied victory in World War II. Robert Buderi states that it was also the precursor of much modern technology.
_____Great Britain made a big effort to develop radar in the years leading up to World War Two. Some people credit them with being pioneers in the field. As it was, the early warning radar system, called "Chain Home", that they built around the British Isles warned them of all aerial invasions. This gave the outnumbered Royal Air Force the edge they needed to defeat the German Luftwaffe during the Battle of Britain.
_____Although radar was originally introduced to give warning of the approach of hostile aircraft it has since been further developed to do much more than its original task. Modern radar equipment plays a vital part in all the operational roles of the RAF: as an aid to accurate bombing; in airborne detection and interception equipment; for the control of guided weapons; as navigational and landing aids; in cloud and collision warning devices. It has many other uses in the civilian as well as in the Service field.
_____Radar is a method of using radio waves to detect the existence of an object and then to find its position in relation to a known point, usually the site of the radar installation.
By means of radar the presence of moving or stationary objects such as aircraft, ships, and landmasses can be detected. In addition, information concerning the exact position of the object (usually referred to as the 'target') and its speed and course, where applicable, can be obtained. The word 'radar' is coined from the initial letters of the phrase: RAdio Detection And Ranging.
_____Radar has been the root of a wide range of achievements since the war, producing a veritable family tree of modern technologies. Because of radar, astronomers can map the contours of far-off planets, physicians can see images of internal organs, meteorologists can measure rain falling in distant places, air travel is hundreds of times safer than travel by road, long-distance telephone calls are cheaper than postage.
2. Principles of radiolocation
_____2.1. General principles of radiolocation
_____Radiolocating is the process of finding the location of something through the use of radio waves. It generally refers to passive uses, particularly radar — as well as detecting buried cables, water mains, and other public utilities. It is similar to radio navigation, but radiolocation usually refers to passively finding a distant object rather than actively one's own position. Both are types of radio determination. Radiolocation is also used in Real Time Locating Systems (RTLS) for tracking valuable assets.
_____Conventional radar systems comprise a collocated transmitter and receiver, which usually share a common antenna to transmit and receive. A pulsed signal is transmitted and the time taken for the pulse to travel to the object and back allows the range of the object to be determined.
_____In a passive radar system, there is no dedicated transmitter. Instead, the receiver uses third-party transmitters in the environment, and measures the time difference of arrival between the signal arriving directly from the transmitter and the signal arriving via reflection from the object. This allows the bistatic range of the object to be determined. In addition to bistatic range, a passive radar will typically also measure the bistatic Doppler shift of the echo and also its direction of arrival. These allow the location, heading and speed of the object to be calculated. In some cases, multiple transmitters and/or receivers can be employed to make several independent measurements of bistatic range, Doppler and bearing and hence significantly improve the final track accuracy.
_____The radar antenna, transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to antenna which is usually located at the same site as the transmitter. The time it takes for the reflected waves to return to the dish enables a computer to calculate how far away the object is, its radial velocity and other characteristics.
_____Electromagnetic waves reflect from any large change in the dielectric or diamagnetic constants. This means that a solid object in air or a vacuum, or other significant change in atomic density between the object and what is surrounding it, will usually scatter radar (radio) waves. This is particularly true for electrically conductive materials, such as metal and carbon fiber, making radar particularly well suited to the detection of aircraft and ships.
_____One way to measure the distance to an object is to transmit a short pulse of radio signal (electromagnetic radiation), and measure the time it takes for the reflection to return. The distance is one-half the product of round trip time (because the signal has to travel to the target and then back to the receiver) and the speed of the signal. Since radio waves travel at the speed of light (186,000 miles per second or 300,000,000 meters per second), accurate distance measurement requires high-performance electronics._____The velocity of electromagnetic waves is a constant value of 300.000.000 m/s. When we calculate the distance, we need to consider a double distance: forward and back. Time can be measured with specific devices. Once we know the velocity and time, we can calculate the distance.
V – velocity
D – distance
t - time
_____In most cases, the receiver does not detect the return while the signal is being transmitted. Through the use of a device called a duplexer, the radar switches between transmitting and receiving at a predetermined rate. The minimum range is calculated by measuring the length of the pulse multiplied by the speed of light, divided by two. In order to detect closer targets one must use a shorter pulse length.
_____A similar effect imposes a maximum range as well. If the return from the target comes in when the next pulse is being sent out, once again the receiver cannot tell the difference. In order to maximize range, longer times between pulses should be used, referred to as a pulse repetition time (PRT), or it’s reciprocal, pulse repetition frequency (PRF).
_____These two effects tend to be at odds with each other, and it is not easy to combine both good short range and good long range in a single radar. This is because the short pulses needed for a good minimum range broadcast have less total energy, making the returns much smaller and the target harder to detect. This could be offset by using more pulses, but this would shorten the maximum range again. So each radar uses a particular type of signal. Long-range radars tend to use long pulses with long delays between them, and short range radars use smaller pulses with less time between them. This pattern of pulses and pauses is known as the pulse repetition frequency (or PRF), and is one of the main ways to characterize a radar. As electronics have improved many radars now can change their PRF thereby changing their range. The newest radars fire 2 pulses during one cell, one for short range 10 km / 6 miles and a separate signal for longer ranges 100 km /60 miles.
_____The distance resolution and the characteristics of the received signal as compared to noise depend heavily on the shape of the pulse. The pulse is often modulated to achieve better performance using a technique known as pulse compression.
_____Radar waves scatter in a variety of ways depending on the size (wavelength) of the radio wave and the shape of the target. If the wavelength is much shorter than the target’s size, the wave will bounce off in a way similar to the way light is reflected by a mirror. If the wavelength is much longer than the size of the target, the target is polarized (positive and negative charges are separated), like a dipole antenna. Early radars used very long wavelengths that were larger than the targets and received a vague signal, whereas some modern systems use shorter wavelengths (a few centimeters or shorter) that can image objects as small as a loaf of bread.
_____Another form of distance measuring radar is based on frequency modulation. Frequency comparison between two signals is considerably more accurate, even with older electronics, than timing the signal. By changing the frequency of the returned signal and comparing that with the original, the difference can be easily measured.
_____This technique can be used in continuous wave radar, and is often found in aircraft radar altimeters. In these systems a “carrier” radar signal is frequency modulated in a predictable way, typically varying up and down with a sine wave or saw tooth pattern at audio frequencies. _____The signal is then sent out from one antenna and received on another, typically located on the bottom of the aircraft, and the signal can be continuously compared using a simple beat frequency modulator that produces an audio frequency tone from the returned signal and a portion of the transmitted signal.
_____Since the signal frequency is changing, by the time the signal returns to the aircraft the broadcast has shifted to some other frequency. The amount of that shift is greater over longer times, so greater frequency differences mean a longer distance, the exact amount being the “ramp speed” selected by the electronics. The amount of shift is therefore directly related to the distance traveled, and can be displayed on an instrument. This signal processing is similar to that used in speed detecting Doppler radar.
_____A further advantage is that the radar can operate effectively at relatively low frequencies, comparable to that used by UHF television. This was important in the early development of this type when high frequency signal generation was difficult or expensive.
_____A new terrestrial radar uses low-power FM signals that cover a larger frequency range. The multiple reflections are analyzed mathematically for pattern changes with multiple passes creating a computerized synthetic image. Doppler effects are not utilized which allows slow moving objects to be detected as well as largely eliminating “noise” from the surfaces of bodies of water. Used primarily for detection of intruders approaching in small boats or intruders crawling on the ground toward an objective.
_____We can’t talk about radiolocation principles without remind on the: Interference, noise, clutter and jamming.
2.2. Interference. Radar systems must overcome unwanted signals in order to focus only on the actual targets of interest. These unwanted signals may originate from internal and external sources, both passive and active. The ability of the radar system to overcome these unwanted signals defines its signal-to-noise ratio (SNR). SNR is defined as the ratio of a signal power to the noise power within the desired signal.
_____In less technical terms, SNR compares the level of a desired signal (such as targets) to the level of background noise. The higher a system’s SNR, the better it is in isolating actual targets from the surrounding noise signals.
2.3. Noise. Signal noise is an internal source of random variations in the signal, which is generated by all electronic components. Noise typically appears as random variations superimposed on the desired echo signal received in the radar receiver. The lower the power of the desired signal, the more difficult it is to discern it from the noise (similar to trying to hear a whisper while standing near a busy road). Noise figure is a measure of the noise produced by a receiver compared to an ideal receiver, and this needs to be minimized.
_____Noise is also generated by external sources, most importantly the natural thermal radiation of the background scene surrounding the target of interest. In modern radar systems, due to the high performance of their receivers, the internal noise is typically about equal to or lower than the external scene noise. An exception is if the radar is aimed upwards at clear sky, where the scene is so “cold” that it generates very little thermal noise.
_____There will be also flicker noise due to electrons transit, but depending on 1/f, will be much lower than thermal noise when the frequency is high. Hence, in pulse radar, the system will be always heterodyne.
2.3. Clutter refers to radio frequency (RF) echoes returned from targets which are uninteresting to the radar operators. Such targets include natural objects such as ground, sea, precipitation (such as rain, snow or hail), sand storms, animals (especially birds), atmospheric turbulence, and other atmospheric effects, such as ionosphere reflections and meteor trails. _____Clutter may also be returned from man-made objects such as buildings and, intentionally, by radar countermeasures such as chaff.
Some clutter may also be caused by a long radar waveguide between the radar transceiver and the antenna. In a typical plan position indicator (PPI) radar with a rotating antenna, this will usually be seen as a “sun” or “sunburst” in the centre of the display as the receiver responds to echoes from dust particles and misguided RF in the waveguide. Adjusting the timing between when the transmitter sends a pulse and when the receiver stage is enabled will generally reduce the sunburst without affecting the accuracy of the range, since most sunburst is caused by a diffused transmit pulse reflected before it leaves the antenna.
_____While some clutter sources may be undesirable for some radar applications (such as storm clouds for air-defense radars), they may be desirable for others (meteorological radars in this example). Clutter is considered a passive interference source, since it only appears in response to radar signals sent by the radar.
_____There are several methods of detecting and neutralizing clutter. Many of these methods rely on the fact that clutter tends to appear static between radar scans. Therefore, when comparing subsequent scans echoes, desirable targets will appear to move and all stationary echoes can be eliminated. Sea clutter can be reduced by using horizontal polarization, while rain is reduced with circular polarization (note that meteorological radars wish for the opposite effect, therefore using linear polarization the better to detect precipitation). Other methods attempt to increase the signal-to-clutter ratio.
2.4. Constant False Alarm Rate (CFAR, a form of Automatic Gain Control, or AGC) is a method relying on the fact that clutter returns far outnumber echoes from targets of interest. _____The receiver’s gain is automatically adjusted to maintain a constant level of overall visible clutter. While this does not help detect targets masked by stronger surrounding clutter, it does help to distinguish strong target sources. In the past, radar AGC was electronically controlled and affected the gain of the entire radar receiver. As radars evolved, AGC became computer-software controlled, and affected the gain with greater granularity, in specific detection cells.
_____Clutter may also originate from multipath echoes from valid targets due to ground reflection, atmospheric ducting or ionospheric reflection/refraction. This clutter type is especially bothersome, since it appears to move and behave like other normal (point) targets of interest, thereby creating a ghost. In a typical scenario, an aircraft echo is multipath-reflected from the ground below, appearing to the receiver as an identical target below the correct one. The radar may try to unify the targets, reporting the target at an incorrect height, or – worse – eliminating it on the basis of jitter or a physical impossibility. These problems can be overcome by incorporating a ground map of the radar’s surroundings and eliminating all echoes which appear to originate below ground or above a certain height. In newer Air Traffic Control (ATC) radar equipment, algorithms are used to identify the false targets by comparing the current pulse returns, to those adjacent, as well as calculating return improbabilities due to calculated height, distance, and radar timing.
2.5. Jamming. Radar jamming refers to radio frequency signals originating from sources outside the radar, transmitting in the radar’s frequency and thereby masking targets of interest. _____Jamming may be intentional, as with an electronic warfare (EW) tactic, or unintentional, as with friendly forces operating equipment that transmits using the same frequency range. Jamming is considered an active interference source, since it is initiated by elements outside the radar and in general unrelated to the radar signals.
_____Jamming is problematic to radar since the jamming signal only needs to travel one-way (from the jammer to the radar receiver) whereas the radar echoes travel two-ways (radar-target-radar) and are therefore significantly reduced in power by the time they return to the radar receiver. Jammers therefore can be much less powerful than their jammed radars and still effectively mask targets along the line of sight from the jammer to the radar (Mainlobe Jamming). Jammers have an added effect of affecting radars along other lines of sight, due to the radar receiver’s side lobes (Sidelobe Jamming).
3. Radar engineering
Usually a radars components are:
-A transmitter that generates the radio signal with an oscillator such as a klystron or a magnetron and controls its duration by a modulator.
-A waveguide that links the transmitter and the antenna.
-A duplexer that serves as a switch between the antenna and the transmitter or the receiver for the signal when the antenna is used in both situations.
-A receiver. Knowing the shape of the desired received signal (a pulse), an optimal receiver can be designed using a matched filter.
-An electronic section that controls all those devices and the antenna to perform the radar scan ordered by a software.
-A link to end users.
_____The transmitter generates the radio signal, and moves them through the duplexer to antenna. Antenna guides the waveform in ether like a directional beam.
_____When the beam meets the target (e.g. aircraft), some of its energy is reflected back on the antenna. From the antenna through the waveguide and duplexer, the reflected signal arrives at the receiver. The receiver amplifies the signal, processes it and prepares it for the signal processor. The signal processor compares and analyzes the demodulated signal and its phase. _____The software on the server does the hard job: it analyzes the signal, it creates a clutter map, carries out a spectral analysis and other tasks. In the end a video signal is created by the alpha server. The video signal is both displayed on the user console and sent from network to Control Center.
Thursday, June 4, 2009
How you make a captcha, antibot protection
A lot of people ask for what is captcha?
Acronym: CAPTCHA=Completely Automated Public Turing test to tell Computers and Humans Apart
He is the most easy way to make difference between Human and Bot. Sometimes he bother us, but he make his job.
A CAPTCHA system is a means of automatically generating new challenges which:
Current software is unable to solve accurately.
Most humans can solve.
Does not rely on the type of CAPTCHA being new to the attacker.
Most requently, a CAPTCHA features an image file of slightly distorted alphanumeric characters.
A human can usually read the characters in the image without too much difficulty. A bot program is able to recognize that the content contains an image , but it has no idea what the image is.
To accomodate the visually-impaired, some CAPTCHAs use audio files. In such a system, the human listens to a series of letters or short words and types what he hears to prove he is not a bot.
Acronym: CAPTCHA=Completely Automated Public Turing test to tell Computers and Humans Apart
He is the most easy way to make difference between Human and Bot. Sometimes he bother us, but he make his job.
A CAPTCHA system is a means of automatically generating new challenges which:
Current software is unable to solve accurately.
Most humans can solve.
Does not rely on the type of CAPTCHA being new to the attacker.
Most requently, a CAPTCHA features an image file of slightly distorted alphanumeric characters.
A human can usually read the characters in the image without too much difficulty. A bot program is able to recognize that the content contains an image , but it has no idea what the image is.
To accomodate the visually-impaired, some CAPTCHAs use audio files. In such a system, the human listens to a series of letters or short words and types what he hears to prove he is not a bot.
Monday, May 11, 2009
Antivirus top
Antivirus Off-line
offerd by: http://www.toptenreviews.com/
offerd by: http://www.about.com/
Ofline antivirus
offerd by: http://www.toptenreviews.com/
offerd by: http://www.about.com/
Ofline antivirus
Sunday, May 3, 2009
Windows Registry Guide
Just some words about Windows registry
_____The Windows Registry is a database which stores critical settings and options for Microsoft Windows operating systems, and help the system administrators to manage better one PC station.
_____It contains information and settings for hardware, operating system software, most non-operating system software, network and per-user settings. Windows Registry offer a path to use and manage etire resources of one system. With the Registry you can control how the resources are used and who can have access on they.
_____A lot of security problems can be resolved with Windows Registry, you can easely to allow or interdict the access on the sistem resources (hardware or software resources).
_____The Registry replace the most part of *.ini files, used to configurate the systems in the earlier version of Windows or MS-DOS, such as Autoexec.bat and Config.sys.
_____Today exists some versions of the Registry, with some diferences between they.
_____When we talk about Registry, we need to understand two basic elements: keys and values.
_____Each key has a name consisting of one or more printable characters. Key names are not case sensitive. Key names cannot include the backslash character (\), but any other printable character can be used. Value names and data can include the backslash character.
_____The name of each subkey is unique with respect to the key that is immediately above it in the hierarchy. Key names are not localized into other languages, although values may be.
_____Registry Keys are similar to folders - in addition to values, each key can contain subkeys, which may contain further subkeys, and so on. Keys are referenced with a syntax similar to Windows' path names, using backslashes to indicate levels of hierarchy. E.g. HKEY_LOCAL_MACHINE\Software\Microsoft\Windows refers to the subkey "Windows" of the subkey "Microsoft" of the subkey "Software" of the HKEY_LOCAL_MACHINE key.
_____Registry Values are name/data pairs stored within keys. Values are referenced separately from keys. Value names can contain backslashes but doing so makes them difficult to distinguish from their key paths. The Windows API functions that query and manipulate registry values take value names separately from the key path and/or handle that identifies the parent key. _____Each value consists of a value name and its associated data.
_____A registry tree can be 512 levels deep. You can create up to 32 levels at a time through a single registry API call.
_____Ordinarily, you do not need to make changes to the registry. The registry contains complex system information that is vital to your computer, and an incorrect change to your computer's registry could render your computer inoperable. However, a corrupt registry file might require changes.
_____We strongly recommended that you back up the registry before making any changes and that you only change values in the registry that you understand or have been instructed to change.
_____You must be logged on as an administrator to perform these steps. If you are not logged in as an administrator, you can only change settings that apply to your user account.
_____Before you make changes to a registry key or subkey, we recommend that you export, or make a backup copy of, the key or subkey. You can save the backup copy to a location you specify, such as a folder on your hard disk or a removable storage device. If you make changes that you want to undo, you can import the backup copy.
_____Prior editing the registry, it's a good idea to create a Restore point using System Restore. The restore point contains information about the registry, and you can use the restore point to undo changes to your system. System Restore helps you restore your computer's system files to an earlier point in time. It's a way to undo system changes to your computer without affecting your personal files, such as e-mail, documents, or photos. System Restore is not intended for backing up personal files, so it cannot help you recover a personal file that has been deleted or damaged. You should regularly back up your personal files and important data using a backup program.
_____Every time when you turn off your computer off and Windows shuts down successfully, important system settings are saved in the registry. You can use those settings to start your computer if a problem occurs. For example, if a new driver for your video card is causing problems, or an incorrect registry setting is preventing Windows from starting correctly, you can restart your computer using Last Known Good Configuration.
_____The Windows Registry is a database which stores critical settings and options for Microsoft Windows operating systems, and help the system administrators to manage better one PC station.
_____It contains information and settings for hardware, operating system software, most non-operating system software, network and per-user settings. Windows Registry offer a path to use and manage etire resources of one system. With the Registry you can control how the resources are used and who can have access on they.
_____A lot of security problems can be resolved with Windows Registry, you can easely to allow or interdict the access on the sistem resources (hardware or software resources).
_____The Registry replace the most part of *.ini files, used to configurate the systems in the earlier version of Windows or MS-DOS, such as Autoexec.bat and Config.sys.
_____Today exists some versions of the Registry, with some diferences between they.
_____When we talk about Registry, we need to understand two basic elements: keys and values.
_____Each key has a name consisting of one or more printable characters. Key names are not case sensitive. Key names cannot include the backslash character (\), but any other printable character can be used. Value names and data can include the backslash character.
_____The name of each subkey is unique with respect to the key that is immediately above it in the hierarchy. Key names are not localized into other languages, although values may be.
_____Registry Keys are similar to folders - in addition to values, each key can contain subkeys, which may contain further subkeys, and so on. Keys are referenced with a syntax similar to Windows' path names, using backslashes to indicate levels of hierarchy. E.g. HKEY_LOCAL_MACHINE\Software\Microsoft\Windows refers to the subkey "Windows" of the subkey "Microsoft" of the subkey "Software" of the HKEY_LOCAL_MACHINE key.
_____Registry Values are name/data pairs stored within keys. Values are referenced separately from keys. Value names can contain backslashes but doing so makes them difficult to distinguish from their key paths. The Windows API functions that query and manipulate registry values take value names separately from the key path and/or handle that identifies the parent key. _____Each value consists of a value name and its associated data.
_____A registry tree can be 512 levels deep. You can create up to 32 levels at a time through a single registry API call.
_____Ordinarily, you do not need to make changes to the registry. The registry contains complex system information that is vital to your computer, and an incorrect change to your computer's registry could render your computer inoperable. However, a corrupt registry file might require changes.
_____We strongly recommended that you back up the registry before making any changes and that you only change values in the registry that you understand or have been instructed to change.
_____You must be logged on as an administrator to perform these steps. If you are not logged in as an administrator, you can only change settings that apply to your user account.
_____Before you make changes to a registry key or subkey, we recommend that you export, or make a backup copy of, the key or subkey. You can save the backup copy to a location you specify, such as a folder on your hard disk or a removable storage device. If you make changes that you want to undo, you can import the backup copy.
_____Prior editing the registry, it's a good idea to create a Restore point using System Restore. The restore point contains information about the registry, and you can use the restore point to undo changes to your system. System Restore helps you restore your computer's system files to an earlier point in time. It's a way to undo system changes to your computer without affecting your personal files, such as e-mail, documents, or photos. System Restore is not intended for backing up personal files, so it cannot help you recover a personal file that has been deleted or damaged. You should regularly back up your personal files and important data using a backup program.
_____Every time when you turn off your computer off and Windows shuts down successfully, important system settings are saved in the registry. You can use those settings to start your computer if a problem occurs. For example, if a new driver for your video card is causing problems, or an incorrect registry setting is preventing Windows from starting correctly, you can restart your computer using Last Known Good Configuration.
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