That's something you have to look out for too. Some of these things hide themselves from the virus scan (I'd tell you how, but that's a bit beyond my knowledge at present) and reinstall themselves if they get deleted
That's why I say go to someone's page (AVG, Symantec, etc.) and find the details on it. Then you can poke around and see if it's really gone or just hiding. Once these things hit, the pros do a good job of tearing them apart and making the details available.