This is a file that provides information to anti virus software to find and repair virus es. The definition file s tell the scanner what to look for to spot virus es in infected file s. Most scanners use separate file s in this manner instead of encoding the virus patterns into the software, to enable easy updating. Learn more in: Developments and Defenses of Malicious Code. Find more terms and definitions using our Dictionary Search. Virus Definition File subscription service appears in:.
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Powered by Higher Logic. Though any virus detecting software can detect viruses, we need to know that there are instances when viruses and malware remain undetected.
The post aims to give you a brief idea on the situation when your antivirus may fail to detect the presence of malware in your computer.
Most of the virus detection software depends on virus definition stored in the virus definition file. Each virus is written with specific a set code which is also called signature or fingerprint. The virus definition file contains that signature a code snippet. When the antivirus software starts scanning it look for specific signature in the files and applications. If there it does not find any known signature in the file, it declares it safe.
No contents of this site is permitted to be published to anywhere else in the Internet. In large sites and large networks, the patch procedure is time consuming. Usually the whole network must be taken down, preventing several users from working. This costs money in time loss. So network managers are careful when applying patches, even because not all patches assures better performance. A patch may also contain incompatibilities and cause problems.
Security holes must be patched, nevertheless. Many websites were hacked exactly because their web servers were running under old software with well—known holes. In home computers, applying patches usually do not take more than 5 to 10 minutes. They might cause problems, but the danger of using programs with security holes does not compensate the trouble. Web browsers and the operating systems deserve special attention.
In Microsoft Windows 9x, there is the Windows Update facility, which connects to Microsoft servers and detects whichever updates are available and needed. The system, if authorized by the user, then downloads the patches and updates itself. Simple and very important, because most security holes do give a hacker access to local files. Some just require the user to connect to a website or open or view an email message. The last security hole discovered by the famous bug-hunter Georgi Guninsky affects Microsoft Outlook Express.
It concerns the compressed help file format for this program. A hacker can embed a script in one such file, and a security flaw will allow the script to access local files or even execute attached files to the email message, without user intervention. The script will run simply by viewing the email message or accessing a web page with the script , revealing the potential danger of these security flaws.
The patch was released short after the hole was discovered. Another form of exploit that can affect any kind of program that has the hole is called buffer overrun. Many programs and the operating system, in order to execute actions, store information briefly in a buffer, which has usually limited size.
A buffer is needed because data is never processed at the same speed it is fed. So, data must be stored until it can be processed. For example, the keyboard has a buffer of its own. Even when the computer is performing some operation that seems to lock it, keys pressed between this time will be saved and will appear on the screen after the last process is concluded in a word processor, for instance.
The problem resides when the buffer is full. When it happens, some programs will simply refuse more data, discarding the excess. Others will signal the source, others might erase the whole buffer. And some might behave in completely unpredicted and weird ways because the programmers might have never imagined that that particular buffer would overflow.
A security flaw found a time ago in Internet Explorer, a buffer-overrun type, was very interesting. A link in a web page could be made with several characters, number enough to overflow the internal browser buffer for hyperlinks. Clicking on the link would cause the buffer overrun, and the additional characters would be executed!
If an actual program were properly embedded in the hyperlink, it would execute in the local computer, under no control.
All programs must be tested for virus before they are executed or installed. When an antivirus is installed, this test procedure is done automatically, if the antivirus is configured correctly. The source is everything when it comes to computer viruses. If the origin of a program is suspicious, caution must be doubled. There are preferred sources from which viruses spread.
Mainly email, IRC channels, newsgroups, and warez distribution sites. IRC channels are perhaps the most promiscuous places. The best attitude is simply refuse to accept any file coming from IRC users, unless it is well known, or it is a picture file which is, to this date, completely harmless.
Virus programmers usually start spreading by sending the virus to IRC users or to newsgroups. The first Palm virus originated from the newsgroups. The safest attitude, here, is to be paranoid.
A file received from an unknown sender should be simply erased. The risk is rarely worthwhile, and unknown, good faith people seldom send files upon first contact. Nevertheless, files received from friends or known people, especially from email, can be suspicious. Worms rely on the trust users put on known senders, by maliciously using the address book stored in the computer and sending themselves to every address.
Text or picture files with extension. Scripts cannot be embedded into these files; nothing is therefore executed. If the operating system is Windows 9x, it must be configured to show all file extensions. By default, Windows hides file extensions, making it difficult to promptly detecting the file type. Remember, a virus can only infect if executed. If a program with a virus has its extension changed to. A double click on one such file would just open a notepad-type program and the user would just see a bunch of meaningless characters displayed.
Files with. They can house macros or scripts that are executed by the word processor, such as Word or WordPerfect. Macros might be viruses. The word processors may have the macro execution capabilities disabled, or may be configured to automatically call the antivirus each time a file is opened.
Even then, if the source of the file is suspicious, a program such as the Wordpad, which comes with Windows 9x, can open the file safely, since Wordpad is unable of processing macros or scripts.
Files with extensions. All of these, but the. Files with extension. They might, however, contain virus, as it was recently proved with. If the source of those files cannot be trusted, the best measure is to erase them. Any files with the extensions above must be tested for virus and opened with caution. If the HTML page has malicious scripts or applets or active controls that successfully override the antivirus and browser firewalls, the computer might be infected.
If an executable file is received from an unknown sender, there is no doubt: it must be erased immediately and never opened. The old lesson taught by every mother applies here: never accept gifts or sweets from strangers. Warez distribution sites might contain two dangers: one of them is the fact they distribute pirate software, which is illegal.
Second, the warez might be a trojan horse, concealing malicious code within. Warez zone is a no-law zone. A low-risk behavior, therefore, if the user usually connects to IRC channels or newsgroups, is to keep business to posting only. Or accept text and picture files only. An innocent looking floppy disk borrowed from a friend might represent the destruction of all files in a computer. It is common that corporations and schools define rules to the manipulation of disks around their computers.
The main cause of virus infection in corporations is an employee who brings an infected disk, or receives an infected email.
In a network or LAN, files in a computer hard disk can be seen or opened by another computer in the network. Therefore, if these files are infected, the computer that opens the files the client will also be infected. The protection measure here is to install antivirus programs in every computer in the network.
Finally, at least every 15 or 20 days, with the antivirus properly updated, the user must command a full virus scan in all files stored in the computer hard disk.
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