Code for Antivirus

There's a C# antivirus project over at CodePlex:
http://www.codeplex.com/CSAntivirus/Release/ProjectReleases.aspx?ReleaseId=12437 
If you don't mind projects in other languages, then there are a lot more at SourceForge:

http://sourceforge.net/search/index.php?words=%28antivirus%29+AND+percentile%3A%5B090.00+TO+100.00%5D&sort=score&sortdir=desc&type_of_search=soft
One of these, Simple Machine Protect, appears to be written in VB6.

I don't know if this is any good but it looked interesting; it is written in C++ with a C# front end:  http://msdn.microsoft.com/en-us/library/bb204055(EXCHG.80).aspx