Dale,
I had a feeling that you were out of your depth with your last questions (the ones i assisted you with), and this question has now confirmed that you haven't got a clue what you were doing when it comes to virus identification and scanning.
The subject is a very complex one and if you really should have investigated the subject matter fully before diving in and writing code.
I am sure there are many experienced programmers on this site, that wouldn't even entertain the idea of writing virus scanning software.
You should do a Google search for "White Paper" and "Virus Scanning" or "Virus Identification", and you will find some interesting papers on the subject.
Here is one that shows you that there is more to it than you already think;
http://www.crswann.com/2-NetSecurity/VirusDetectionTechnology(McAfee).pdf[
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Anyway, back to your original question;
A virus signature is simply a collection or sequence of bytes that are found in a file that are tell tales of the particular virus. e.g. See this page which details a standard test file which every virus scanner should detect.
http://www.eicar.org/anti_virus_test_file.htm[
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Virus companies spend years building up databases of signatures, and are actively scanning the internet and receiving files suspect of containing new virus so they can incorporate the signatures into there products.
As you will see reading the links i have attached, there is more to it than simply what you have been programming to date.
If you want my honest opinion, i would say STOP now, and find something to code which you fully understand and are more likely to make money on.
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