I assume out of the 200 Million Avast users there is a lot of them on Windows 8.x. 
I luckily am on W7 still but I think it would be nice if Avast Team member responded to this threadā¦seems a fairly important issue. :o Can one of the Super Posters ping/PM the key Avast Team folks that review the Forum ? ā¦I have no contacts else I would.
Donāt worry Iāve seen a couple of them already reading the thread. A minute ago petr.chytil was doing it.
same to me with KB3000850 AND AVAST! installed.
It would be urgent that AVAST Support recognizes the problem. Otherwise a lot of people uninstall AVAST and wait until a fix exists.
Folks from AVAST, check it please
I to am running Avast and KB3000850 with 8.1. Stuck on rebooting since installing this update. I have ran sfc /scannow and all is fine according to system files.
Is the only solution to uninstall avast to clear up this issue? while things get fixed either Avast/ Microsofts end.
For KB3000850 on 8.1 has anyone tried to disable Avast Shields and also go into Avast UI under Settings>Troubleshooting and uncheck Self Defense Moduleā¦THEN try Windows Update. You can re-enable all this after reboot.
I would try and post but Iām all W7.
I tried reinstalling Avast from the standalone installer and it re-borked my system.
Avast 2015 (10.0.2208.712) is now fundamentally incompatible with Windows 8.1, fully updated with the latest optional update.
-Noel
I am just downloading that update now, I have an image just in case 
I will let you know how it goes
A. Make sure you have the latest AvastClear for version 10 on hand.
B. Youāll need to run it without booting into Safe Mode first.
C. Youāll want to run it again in Safe Mode after the above restores rebootability.
Amazingly, everything else seems to work with the KB installed and Avast not.
-Noel
Experienced Same issues, Mine hung on Preparing PC, donāt turn off computer for over an hour, powered off, and restarted hard, and couldnāt open Programs and Features, IE Window wouldnāt work, Skype wouldnāt work on my 8.1 64bit with Media Center Machine.
Laptop couldnāt access for a while Avast forum, so i ended up doing a full hard disk wipe, and starting full reload, Windows 7 64bit, then Windows 8.0, then finally if all goes well 8.1 Install via the app store, only way to do it for me, wonāt take my key any other way.
Will make room for image after all this on external drive, this is a major pain
Currently I have Avast 10.0.2208.712.
Uninstalled and reinstalled didnāt work with Windows 8.1 64 updated.
What Iāve done.
[ol]- using CCleaner uninstall (canāt get normal uninstall to work).
- using safemode avastclean.
- removing vboxasw manually.[/ol]
No need for that the image is only a few hours old
Is there any logs or anything we can provide to get this issue resolved asap ?
So I just received a useless reply from Avast tech support about this. I opened a ticket last night saying that since KB3000850 Windows Explorer freezes, windows wonāt cleanly shut down, etc. ā until I uninstalled Avast.
I suggested that Avast didnāt break Windows, that Windows broke Avast ā but that nevertheless Avast will need to try to fix Avast to remove the incompatibility.
Hereās the response I received from support - I replied and told him his answer didnāt help, and that I was not getting a false-positive virus report but freezes/crashes/crap.
[i]Hello,
this would be most probably the new malicious software removal feature from Windows. It is common that one security software is finding the positive threats in other security software`s database which contains samples of viruses, as every antivirus application do. So that is why is not recommended to use two different antiviruses on one machine, because there will be 100% conflicts and it can cause damage of your system. Do not worry Avast is 100% threat clean.
Best Regards
Albert Fiala[/i]
How do you do the above in bold ? ā¦Iām assuming you canāt get into regular Windows or Safe Mode ?
November roll up installed first https://support2.microsoft.com/kb/3000850?wa=wsignin1.0 now about to install the dreaded KB3000850
Installed KB3000850 and KB3011780 when they were first released 11/18 and have not had any issues at all.
Win 8.1 x64
I do not have NG or any of the other tools installed.
Interesting noteā¦I only have shields installedā¦nothing elseā¦but again Iām only W7.
Suffered the same problems as other users after applying the optional update.
Then after removing avast by using the avastclear app while in Safe mode, the problems have gone away.
Clearly it is a conflict between avast and something that has changed with this update.
Gonna go back to the previous restore point and reinstall avast, hopefully the problem can be resolved soon so that the update can be applied without these problems.
It only happens with windows 8.x. My Windows 7 laptops work just fine. There is definitely a problem with KB3000850 and Avast 2015 Internet Security.
What I did was first removed avast. Then I uninstalled the KB3000850 and then reinstalled Avast and all is working again. There is a capability problem between Avast 2015 and KB3000850. Any idea when you will have a fix?
Same problem for me too on Window 8.1 Pro 64bit and Avast Pro 2015. Computer lags, programs not working and computer not being able to restart or shutdown. I removed the update KB3000850 using system restore. Hope Avast or Microsoft has a fix for this problem as soon as possible.