The latest Avira update which bumps your version to 8.2.10.64 and definitions file to 7.11.30.24 will detect

• \windows\system32\dllhost.exe
• \windows\system32\explorer.exe
• \windows\system32\iexplorer.exe
• \windows\system32\notepad.exe
• \windows\system32\regedit.exe
• \windows\system32\rundll32.exe
• \windows\system32\taskeng.exe
• \windows\system32\wuauclt.exe

as being “positives” and will prevent Windows Boot, MS Office, MS Works (or doesn’t in this case) and many other third party software apps.

Luckily the free version does not have the “Pro-Active” module and will not be affected.

Avira Antivirus Premium and Avira Internet Security as well as business editions (Avira Small Business Security Suite, Avira Endpoint Security, and Avira Professional Security) do have it, and thus are affected.

Avira suggests this in the meantime:

“Avira is analyzing and discussing this suspicious behaviour detections with high priority.
Meanwhile, you should see at Realtime Protection report file the processes blocked by Avira ProActiv (Go to Avira Control Center > PC protection > Realtime Protection > Click on Display Report file). Then, follow this workaround.

• Right-click on your Avira systray icon and choose Configure Avira Antivirus Premium 2012 or Avira Internet Security 2012
• Enable Expert Mode
• Go to PC Protection > Realtime Protection > ProActiv > Application Filter > Allowed
• Type each path (from Realtime Protection report file) in the empty field and click Add >>
• Click on Apply > OK”

But that is not a very good solution for folks who can’t boot up.

ZDnet suggests the following:

If you can manage to boot into Windows (try Safe Mode), here are the instructions for disabling ProActiv:

1. Bring up the Task Manager. Hit CTRL + SHIFT + ESC, right-click on the task bar and choose “Start Task Manager,” or hit CTRL + ALT + DEL and click on “Start Task Manager.”
2. Click on File, then “New task (Run…),” type “c:\program files\avira\antivir desktop\avconfig.exe” or equivalent, and then click OK. This will open the Avira Antivirus configuration window.
3. Click on the Expert mode switch at top left.
4. Click Realtime Protection on the left panel and then on Proactiv. Untick the check box for “Enable Proactiv” on the right. Click Apply.
5. Restart your computer.

That isn’t the final solution which will be forthcoming from Avira.

You can find more information here:  http://www.avira.com/en/support-for-home-knowledgebase-detail/kbid/1257

Source:

http://www.zdnet.com/blog/security/avira-antivirus-update-cripples-millions-of-windows-pcs/12129?tag=main;top-stories