What happens when your anti-virus turns on you? The simple answer is your computer stops working.
This was made evident in a recent update to Avira (ironically only affecting the paid versions of the program and apparently only in 32-bit environments). After the update, the AntiVirProActiv component began flagging critical system processes and preventing the computer from booting. In the unlikely case the system did load, Avira began blocking software programs, virtually all executable files including Microsoft Office.
The good news is that the free edition (Avira Anti-Virus Personal) does not include the ProActiv component. Unfortunately, the paid versions do, including the business edition.
So far, it appears as if affected machines are pretty easily fixed by updating Avira yet again, a fixed update was released May 15th, but that was after a supposed fixed update. Avira does give update instructions and a two sentence apology. http://www.avira.com/en/proactiv-application-blocking Also included are instructions to disable ProActiv completely.
While we understand that mistakes happen, there needs to be better communication from companies in situations like this.
If you use one of the paid versions of Avira, please make sure that you are not running software version 126.96.36.199. If you are noticing issues, start a product update. You may need to boot into Windows Safe Mode to get this to work.