It's not just one "bad" update. The last version of Avast 8.x family was stable, fast, had a good UI, wasn't filled with upsells and ads.
That's the version I used on mine, my father's and mother's computers.
Several weeks ago it flagged WS_FTP's DRM module on father's computer as a virus.
Then, more recently, it quarantined Opera browser and some other executables on mother's computer.
At about the same time, it flagged random NVidia driver DLLs on my computer as well.
I restored all files from quarantine and immediately got rid of Avast on all machines. This is planned obsolescence, a move to force us to upgrade to 9.x.
At first, I gave it a shot. Then I loaded the latest 9.x version and saw that it not only kept the messy and yet somehow function-reduced UI from earlier 9.x releases, but it's full of upsells and then an ad pulled out of system tray asking me to buy Avast...
And of course, on my sister's PC, which had "automatic program update" enabled, despite having an initially minimalistic install of 8.x, 9.x came along and installed "grime fighter" and all the other garbage.
That's not how upgrades are supposed to work.
Goodbye Avast, you were good while you were good. Now you joined the ranks of pretty much every other "free" antivirus which are, at best, "potentially unwanted programs" themselves.