I agree wholeheartedly with Fred S, mjt, jbaumann, Tetsuo, Grifter02, timbirr, and am just as livid as supergills. (Schmidthouse and others who have suggested that some users are too ignorant to use a custom install or to uncheck the install Chrome option have no idea what the heck they're talking about. There is simply just no option presented when updating via the UI.)
Those who say "just uninstall it" just don't get it. My computer belongs to me, not to Emsisoft Avast. Surreptitiously installing software on my computer and then expecting me to deal with the cleanup is unethical. Sadly, Emsisoft Avast has been guilty of this highly unethical practice for a long time. It was discussed in this forum over a year ago, when they were piggybacking some other Google software on the UI updater. There is absolutely no excuse for this. It would be simple to offer an opt-out with the UI updater. It would also avoid offending loyal users. Emsisoft Avast has offered no explanation why it treats loyal users (those with Avast already installed) different worse than newcomers (those downloading Avast for the first time).