I don't know what to think honestly, can't tell if all AVs are equally useless against rogue or not...thing is as said it's been reported so many times now that Avast didn't stop a rogue install...and to some extent, this is almost understandable as there's "just" another software install process going on...
adding: it's not just a matter of being able to detect every single threat, Avast seems completely unable to detect any rogue... (I haven't experienced that personally, just read reports).
I wonder if "mode of transport" may be a factor here. I suspect it's riding in a Java applet, since
just prior to the event I noticed a series of little coffee-cup icons (java) marching leftward
along the taskbar.....first one, then two, then three, etc. all by themselves and I hadn't even clicked on anything.
Don't know for sure, but I suspect an innocent-looking javascript may be providing cover for this thing, perhaps unintentionally, lurking in an ad or display on an otherwise OK website.
It completely fooled Avast, before and after.