Had this happen again on another PC
Avast installed Google Chrome without displaying the option to uncheck it. This is what seems to be the cause. Avast 7, if installed through the maintenance function of a previous version may do this under one condition. If that previous version was installed using program defaults, Avast 7 seems to not display the check boxes because those are the new defaults. I've now had this happen on 2 PCs when upgrading through the Avast maintenance function. If you just download the new file and install that way, you get the opportunity to not install Chrome at the same time.