What brand of AV software are you running?
Sorry to be persistant but just to be sure why don't you downoad the free version of AVG antivirus from here: AVG Free - Download antivirus and antispyware software for Windows XP and Vista let it update its virus definitions and let it loose on your system and see what it comes up with. It may find nothing but it's worth checking just in case a virus has managed to slip past your current system.