To the Original Poster (and anyone else)

I had a similar (but even bigger) popup advertising Google Chrome that was caused by my not paying attention during installation and missing a pre-checked box.

I suspect that somewhere sometime you checked (or didn’t un-check) a box that said you wanted to see advertisements of upgrades and special features.

You can see the thread that I started, the offending file (Offers.ini) and my solution and commentary at: http://forum.avast.com/index.php?topic=140849.msg1027907#msg1027907