Many AVG users are now asking help in forum on why they could not run legitimate applications such as Firefox, Microsoft Word, CCleaner, Malwarebytes’ Anti-malware etc. Other users has reported to receive a dialog box that the executable of the program that they are trying to open is is not a valid Win32 application. While some are getting that a .dll file is missing.
All of the above reports started to happen to end-users that has AVG and allowed AVG to delete/quarantine the infection Sheur2 and PSW.Agent.ABTK.
Looking at the sample AVG activity logs by AVG user at BleepingComputers.com shows that AVG has deleted a lot of legitimate files by legitimate applications including Windows Update file wuauclt.exe by Microsoft and even the AVG executables avgcmgr8.exe!
Running the system file checker utility will help but it will not solve the problem because AVG did not only detect system files but executable of third party applications that SFC will not restore.
If you are seeing the said problem, make sure to read the activity log of AVG. Restore the files from AVG vault. Update your AVG definitions soon.
AVG Moderator confirmed on August 28 in a forum post the false alarm and that they have release a new virus detection update.