A faulty update for Avira's paid-for anti-virus software blocks harmless processes and may in some cases stop computers from booting. The update results in the ProActiv behavioural monitoring component becoming oversensitive in its treatment of executable files.
According to user reports, ProActiv blocks trusted system processes such as cmd.exe, rundll32.exe, taskeng.exe, wuauclt.exe, dllhost.exe, iexplore.exe, notepad.exe and regedit.exe. In some cases this results in Windows failing to boot properly. It also appears to be blocking non-OS applications such as Microsoft Office, the Opera web browser and Google's Updater program.
All versions which include the ProActiv behavioural monitoring component are affected, including Avira Antivirus Premium 2012 and the enterprise version; only 32-bit systems are affected, as ProActiv doesn't currently support 64-bit operating systems. On the Avira forum, an employee of a company which runs Avira on one hundred computers complains that, "This update has been pretty catastrophic. The whole company ground to a standstill."
Update: Avira recommends adding exceptions for the affected system processes to the ProActiv's Application filter. However, as the list of processes is rather long, it is still advised for the time being to disable ProActiv.
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