If you're using Avast's anti-virus program on your Windows 8 or 8.1 machine, watch out. Applying the program's latest update along with Microsoft's latest patch for Windows 8 will grind your computer to a halt.
The company posted an explanation of what went wrong on its blog after what was, I'm sure, a few very stressful days:
“We have been able to simulate the problem in our lab and I think we fixed this issue. This Windows updates calls new memory related functions which are not fully compatible with Avast.”
If your computer is running slowly, then you might want to consider using another anti-virus program until Avast comes up with a new version. I recommend Malwarebytes.
For those willing to wait it out, though, the company has pinned down the problem. Rest assured that the fix will be in soon.