[yrio]

What about open source antivirus software like ClamAV?

[exadeci]

It's perfect!

I use http://www.clamwin.com/ which is just an easy way to install it.

There was a pdf about antiviruses that was posted a few month ago IIRC and they all had huge flaws except surprisingly ClamAv which had minor ones.

[floatboth]

Usually used on email servers.