Try these free on-line scans: Trend Micro HouseCall
... java version for Firefox users.BitDefender Free Online Scanner
... requires IE (activeX based)Panda Active Scan
... I have stopped using Panda's free active scan because of the false positives, which I suspect is used as a sales tactic (identifies malware, but doesn't remove it ... )
Use one or more of these as 2nd opinions ... note my caution on Panda's free Active Scan now.
Note: None of these free scanners has found a legitimate virus that Avast has not.