On Thursday morning, the protection programs of AVG incorrectly identified the Windows system file wintrust.dll as a trojan of type "Generic32.FJU". Under certain circumstances, the virus hunting software has also labelled programs as malware if they attempted to access the supposed trojan DLL. The solution is a virus signature update.

Only Windows XP systems were affected by the problem. Users who deleted the file from their system could not boot their computers any more. In this case, to help restore the system, boot it with the Rescue CD and take wintrust.dll from a still functioning system and copy that to C:\Windows\System32\. At least, according to AVG, the anti-virus software did not automatically delete or quarantine the wintrust.dll file, though other files will have to be moved back into place.

The company says it fixed the problem by 12:45 on the same day with updates to virus database number 567 for AVG 9 and 2012 editions and virus database number 6174 for the current 2013 edition.