When I did computer work the 2 best free that I tested were AVG and AVAST. My preference was AVG and still is but have nothing bad to say about AVAST. I have had AVG find infected files that Norton McCafee and TrendMicro never saw.
Get AVG Free here:
http://download.cnet.com/AVG-Anti-Vi...html?tag=mncol
Get AVAST here:
http://download.cnet.com/Avast-Home-...html?tag=mncol