A pattern file is a computer file used to help capture viruses, and it often works in tandem with a larger antivirus program. This type of file usually has small and basic virus definitions loaded on it, so it can help identify viruses, but it rarely has full definitions. To help find viruses, this will copy a small amount of information from a file and, if it tests positive as a virus, then it will pass the information to the antivirus program. Most pattern files are made to work with only one or a limited number of antivirus programs, and there are few generic pattern files. This file does not have full virus definitions, so it is much lighter, which makes it easier to go through other files and extract information.
When an antivirus program is installed, it typically will have a large library of viruses and it will contain the full definition, or code, of each virus so it knows how to identify malicious programs. A pattern file usually does not have a full definition. Rather, it contains partial definitions that will enable it to identify potentially malicious files, but it is not intended to make the final decision on whether a file is dangerous.
To help with the antivirus program’s scanning, the pattern file will float around and copy information from files found in the computer. Most files will be harmless, and the pattern file will move to the next file. If the extracted information is similar to a virus, though, then the pattern file will bring this to the antivirus program’s attention, and the antivirus program will perform a thorough scan of the file.
Most pattern files are not generic, nor are they inherently installed on a computer. They are part of an antivirus program, and most can only work with the same or a similar antivirus program. Even if these files are installed on a computer, if there is not a compatible antivirus program they can alert, then pattern files will not do much good.
While not having full virus definitions and lacking the ability to destroy viruses themselves may seem like a hindrance, this is done to decrease the pattern file’s weight. This file is smaller, so it can easily scan other files without creating a large digital footprint. This also enables it to constantly float around the other files without causing frequent lagging for the user, whereas an antivirus program could cause lags if it is constantly scanning the computer.