How to Build a Virus Scanner
Building a virus scanner takes very specific programming skills, but the general approach is not difficult to understand. A virus scanner uses predefined code samples that are call "signatures." These signatures are compared against other programs on the computer, and if the programs have code that is similar or identical to the signature file, the program is marked as a virus. The design of these signatures and the manner in which they are compared with program files are paramount in the development of a virus scanner.
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Instructions
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Decide what type of viruses you want to scan for. Many types of viruses are being developed every day. Some types will cause data to be destroyed and wreak havoc on a person's computer, while others simply sit in the background and show pop-up ads every few minutes. Different types of viruses require different types of signatures to detect.
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Design signature files that you can use to scan files for a virus. These signature files are usually developed from known virus code, so one approach would be to analyze the code of a known virus file and write a signature file based on that. Then, whenever that virus showed up again in a computer, you would be able to detect it.
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Create a scanning utility that will parse through each file on a computer, and compare that file with the signature files you have created. Generally, only the first portion of files is compared with signature files, since that is usually where virus code is placed. To be more thorough, the scanner can compare the entirety of each file on the computer with each signature file, but this increases the time it takes to scan the computer and makes on-demand scanning (which scans every file the computer opens as it opens it) very resource intensive.
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Tips & Warnings
If you want to build your own virus scanner, you should ensure that you have programming talent or that you hire people who do. Also keep in mind that building a virus scanner is a massive undertaking, since new virus variants are produced every day, so if you want to make sure your scanner is up-to-date, you will have to be constantly analyzing new viruses and creating definition files for them.
