Many .exe, .zip & .rar files shared on the network are infected. I'd stay away from program files. Are you scanning all files that you download with an updated AV, before you open them? You should.

Also check files with Bitzi before download... if other users have rated the file then you'll get some idea of whether it's clean & works.
How to use Bitzi

* WARNING: Viruses on network you should be aware of ! *