An Avast virus definition file update late Wednesday accidentally marked hundreds of legitimate files as threats. The Czech Republic-based publisher Alwil responded quickly, issuing a fix less than six hours later, but some users are still dealing with the aftermath.
Going through Avast's forums, the Avast-written guide for rescuing files falsely marked as threats should be quite simple. Force an Avast update, then from the main interface go to Menu, then Virus Chest. Right-click on the file in the chest you want to resuscitate, choose Scan to double-check that it's not a threat, then right-click on it again and choose Restore. Avast cautions that if that fails, you can choose Extract to put the file back where it came from.
For some instances of the Avast 5 beta and Avast 4.8, this doesn't work. The best solution I've found is the most annoying: run the installation file again. This certainly takes longer, but right now I've been unable to find any other solution that can be applied across the board. The one saving grace about reinstalling is that, at least for the files on my home computer that were affected, I didn't need to reconfigure any of the settings. The KMPlayer, IOBit Smart Defrag, and Find and Run Robot all retained their previous DLLs and other settings.
Keep in mind that this isn't the first over-eager definition file update. Two of the more recent ones include an incident from July that saw an update from Computer Associates flag a Windows XP system file as a virus, and last year AVG falsely identified a file from security provider ZoneAlarm as a virus.
If you're continuing to have problems from the Avast update, let us know in the comments below.