I too have had a problem with Avast and the new windows updates, I have reported it to Avast because I have 3 computers that are running and need the new updates, which I can't do because I can't afford the pc's to crash, as one of them did which is why I am posting this.
I am running Windows 7 (all these pc's are running the same specs) 64 and I am running Avast internet security (which I actually paid for with 3 licenses which is why I'm annoyed) on trying to update windows update the pc just hung on the windows welcome screen, wouldn't go any further, after several restarts trying to get it past the welcome screen still had nothing couldn't even get it to boot into safe mode, so tried some windows tool that is supposed to fix pc's freezes when your trying to update, well that didn't work either, when finally after lots of troubleshooting and lots of investigating I finally got it to boot into safe mode but then lost the ability to use the mouse, when in safe mode everything worked fine but couldn't get past safe mode into normal windows.
Now a little history, several months ago on another update I had a similar problem then a little light went on insode my head and remembering back the only thing that got me back to normal was uninstalling Avast.
So back to present time and lots of hair pulling and lots of curse words used I decided to uninstall Avast in safe mode and then restart pc, voila pc went straight back into windows no dramas, so I had to then reinstall Avast.
I must say though I am quit annoyed with the Avast developers, I paid good money for 3 licenses and reported this problem 2 days ago marked this as emergency on the priority listing and still no response from anyone. So it does go to show whether your using Avast free or a paid version you still have problems, but does kinda make me wonder why I paid for Avast now.