2 laptops with Windows8.1, one work fine after update kb300850 (Samsung intel i5), another dead (HP 455 amd a8-7100),both of them use Avast internet security 2015 (sorry for my english) 
Same problem here on Win 8.1 64bit after yesterday Tuesday update. Waiting for a fix soon
Hi,
I uninstalled it KB3000850. He is guilty as charged. I did and every is working fine, including Avast 2015 Free.
Really the most important update is KB3011780. So, I left installed KB3011780 and KB3014442.
Windows 8.1 Pro w/WMC 64 bits spanish version. Totally updated.
Good luck. Donāt worry, do it!!
What I did:
- Started Windows in Normal Mode
- Uninstalled Avast AV Free through Control Panel (first time the Uninstaller reported error, but the second time it worked) - it takes a while till the uninstaller appears, so be patient.
- Rebooted normally - did not work, so hard reset.
- Rebooted in Safe Mode.
- Used http://www.avast.com/uninstall-utility to remove all Avast software.
- Rebooted in Normal Mode
I did not re-install any Windows Updates, as the standalone installers for the latest updates are saying that the updates are already installed.
Win 8.1 Pro, 64-bit.
Now using Windows Defender 
but everything appears to be working again
Found this out via another site
The 711mb update is Microsoft quiet release of WIndows 8.1 update 3, Details on this link
http://www.winbeta.org/news/microsoft-has-quietly-released-windows-81-update-3-november-update
So perhaps with them quielty releasing it, resulted in Avast not being ready for this?
Iām back with the update installed and no problems at all. I had problems downloading it as MS went unresponsive several times.
But, the install took about 5 minutes and I am now up and running with no problem. Maybe installing the November rollup first resolved any problems
I updated to kb3000850 on windows 8.1.1, on 2 computers both having issues with avast now not loading completely and forget about shuting them down or restartingā¦ much less opening thingsā¦, one is my main the other is a clean install pcā¦
idk if microsoft put out a bad update or what but ive done uninstalled and reinstalled avast to no success whats so ever
Install the November update first, that is what I did https://support2.microsoft.com/kb/3000850?wa=wsignin1.0
Yes but you read about this issue in advance as I can understand. Now my computer is affected by this issue. Uninstalling Avast does fix this issueā¦reinstalling it makes issue appear againā¦
So letās wait for an official statement from Avast and/or Microsoft
Not really as I had the November rollup downloaded ready to install
I donāt follow. You mean you installed KB3000850 before installing the other patch KB3011780 ?
Did you read reply 49?
Sorry, but the November update KB 3000850 is the one being blamed for all the botched systems. So. If essexboy says, he installed it first, it does not make sence in my book. First to what ? Also since English is my second language, I am trying to confirm what he meant by it or did exactly.
i have posted a post on the MS support forums explaining the issue i have in hope either MS can help solve the problem or Avast can find out what is causing the problem and correct it. http://answers.microsoft.com/en-us/windows/forum/windows8_1-windows_update/major-issues-with-kb3000850/5cb4cddd-52da-44af-9fd5-3ae1a72b0b1a The more people who speak up may help in getting this issue fixed sooner i hope.
@Steve33: thanks for pushing MS to look at this riddiculous update. I have experienced the same issue last night and almost wanted to throw the computer out the window considering it took forever to install only to screw up everything.
At one point I was almost certain my hard drive is toast since even opening up System or using Winrar would slow down to snailās pace and the HD light was almost solid. I checked right away in Task Manager and Avast32 process was just hogging the drive. It must be some compatibility issue where Avast if fighting against the introduced update changes/features. Or maybe itās something to do with x86 vs x64 architecture. I am running Windows 8.1 x64 Pro with Media Center.
same thing happened to my systems, both mine are x64 windows 8.1.1 pro and regular doesnt really matterā¦, the uninstaller in safemode saved itā¦
hopefully this all gets straightend out soon, I already put another antivirus on my main pc for now its working great but never really cared for itā¦ at least its something
I think MS never will care about problem with AVAST productsā¦
Only AVAST users report about problems with last update!!!
Iām sure that AVAST will resolve any problem compatibility with any MS products, not MS!
and
Iām wattling the information from AVAST now or even new version AVAST as soon as possible, not any fix update from MS!
AVAST, please give us any info about conflict between AVAST product and last MS update.
Thank you for your business.
I tried installing Avast after the update and Avast seemed to work with no problems at all - until after the first reboot.
Did you reboot after all the installs were done?
-Noel
Iāve also had this problem on my Win 8.1 Lenovo laptop. Everything was fine until the update and then the usual inability to restart that everyone else has had. In addition though I am not able to install or uninstall any programs or make any real system changes. After three attempts to uninstall Avast in safemode using the avastclear I eventually got it to remove Avast.
I can now restart my laptop but it hangs (takes 3 minutes) at sign-in and I still canāt install or uninstall applications.
I have same problem.
I am running Windows 8.1 Pro. Installed Win Update KB3000850 and after restart upon update installation I had all sort of problems, like: cannot open Control Panel, cannot open some files, and computer was so slow that was impossible to work. I have noticed that I did not have avast icon in the notification area upon restart, as well. Shut down did not turn off computer and restart did not worked at all.
After few queries on google I have uninstalled Avast and computer start working normally again. Later, I have reinstalled IS and free version for few times. I have disabled few options during installation like: NG, Secure DNS, Safe zone and some other and that did not resolve anything, computer was sluggish all the time with avast installed.
I have removed avast completely. Now, computer working like a charm.
When we can expect the fix from Avast?