Poissonally, (That's a joke, a pun in 3 directions) I think that more than one virus checker is needed. I use Xoftspy (pirated, cracked) AVG (free edition but thinking of updating to cracked professional or whatever it's called) adaware and spybot. I don't get virii any more.
Also I use Firefox so I don't attract them, and if my friends in low places like Oz started using some sensible msgr software, I wouldn't use msn msgr either and pretty much kill the whole issue.
But then I don't surf porn. I got a beautiful wife, so who needs it?
When I do a major crack thing, though, I ramp up everything since that is the time I get bastard virus things. Last time, a few weeks ago, got a nasty sucker but I killed it dead. Was really really worried about that one. First time for years that one got through, and it was a nasty one, and I was the one who OK'd it, bastard got in while I was coincidentally cracking a game, so I accepted the registry changes thinking it was the game installing. Bastard.
Live and learn. Or don't and die.