I had a similar problem, but I was not even allowed to uncheck the box to install Chrome. All I saw was a flash of a Avast 7 screen, and soon after that a new chrome shortcut on my desktop as I always delete them.
The new installation of Chrome disabled my user installation, and reset the profile settings. This is Google's fault, but again, Avast did stick this installation at the end, and again, I wasn't given a chance to uncheck it, but wasn't given that simple courtesy. I have since removed the system wide installation, and reinstalled the user installation, however the damage to the profile is already done, along with your reputation Avast.
I have to call some other people, and warn them about this Avast Update.