For all fans / users of Avira, seems like they've sent out a problematic update which is causing some problems.
Looks like the impact is to their commercial "paid for" version and there is no mention of their free version in the article.
Avira Antivirus update cripples millions of Windows PCs | ZDNet
Seems like everyone gets their turn in the barrel as this type of thing has happened in the past to a lot of top tier Antivirus vendors often retail and free versions are impacted.
There is some mention of a workaround in the article and a possible fix pending.
Best of luck