What OS and what service pack for that OS?
Avast can't open a packed file to scan it so it says it's corrupted. Google this >
Pick this > 42127 avast
I maintain the hotel's guest computer in the lobby and only use Stinger or ComboFix. They are not full time/real time scanners but if either one picks up on a bug it will not bother to ask you what you want to do. It just stomps the s**t out of the infection and moves on. If you use either one or both, disable any real time protection you have running THEN run these one at a time. Make double dang sure you have disabled any network/internet connections before you run these.
Reboot and re-enable your connections.
If these programs don't find anything worth letting you know about there was nothing there to start with and avast is giving you a false postive.
Stinger > How to Use Stinger | McAfee Free Tools
ComboFix > Bleeping Computer Downloads: ComboFix Download