Security software outfit Avast are trying to figure out why the combination of recent Windows patches and updates to the latter company's software are breaking PCs. Hordes of users have found that their PCs, especially those running Windows 8 and 8.1, grind to a halt after they apply both Microsoft's recent KB3000850 update rollup and Avast's latest automatic updates.

Some users report their PCs won't boot, or take forever to apply patches. The Avast forums record many users venting their spleens. Microsoft's not immune either: a Redmond thread titled Major issues with KB3000850 includes plenty of people wondering why the company issued an update incompatible with third-party software.

That criticism may not be entirely fair, as an Avast staffer has posted the following explanation for the mess:

“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.”
The poster, by the name of “pk”, promised an update to remedy the situation and later reported that the patch was issued last Friday.

A few forum members seem, however, to be having trouble even with the automated patch, reporting a variety of glitches including very slow downloads of the KB3000850 update on machines running Avast.

Whatever the cause, a fair few people are rather upset with both Avast and Microsoft, with the latter company most often felt to be in the wrong.

Microsoft forum moderator Rohit Siddegowda offers suggestions for overcoming the issues created by KB3000850 here

Windows 8.1 with Avast and KB3000850 equals bricked OS