Apparently this update KB3000850 is interacting with Avast users and some not Avast users to wreck their systems. Uninstalling it is the key to getting the system back to normal and waiting till they fix the issue...dont download.
I have Avast and when I installed the 700mb update I didn't notice any conflicts. I do have a small increase in shutdown time. I see that many have problems and don't have Avast. There must be some other things that matter such as what other programs are running in the background and the way Windows is configured. Who knows, but with an unusual update of over 700mb I would suspect that things can go wrong. When I saw that huge size, I made an image backup before updating just to be on the safe side. LOL