this might sound very very stupid, but i have in fact found a virus names 'AIDS' on my computer, i didnt know what it did because i only discovered it in the Norton Quarantine.
Also a little while back i was searching pawn shops and a popup appeared on my computer, it had no way to close except by hitting 'accept' so i did. what it did was it changed my background to a neon blue with an ad for a virus program, every now and then it would have pop ups about the program and it disabled all sweeper programs and many other random features including the internet. we had to eventually call microsoft so they could fix it for us (free of charge too! how nice of them.)