Not when I was using Windows did I use antivirus - the best protection against them is to be careful - nor in these years with Mac have I used any of the available ones, but if you are one of those who use them, Avast! offers you a free one.
After being installed on millions of Windows computers, avast! Free Antivirus for Mac is available and can be downloaded from the link that a few words ago I have put, in order to have extra protection on the Mac.
It contains a really good design and is updated with the most recent databases, but do not forget that it is a beta and that as such it can fail.
Source | TUAW