don't know but most free ones fail ... well from my experience.
But is the a free one? Or at least a temporary trial or something? I know Macfee (Not sure how you spell it) has a free 90 day trial I might use.
Don't download gay research, then you won't have an problems.
AVG free is nice too.
Spybot:S&DWith it's new upgrade, Tea Timer, I searches for viruses and various other problems before they can activate and go into hideing. I only have 1 virus but it is disabled and only opens up IE which I can close at any time with Task manager.