I have been periodically seeing “404 not found” type messages while doing engine/virus updates using v5.0.677 (FREE)?
Is your internet connection stable?
Did you have another A/V product on your computer before installing Avast?
Internet is as stable as it can be w/ COMCAST! NO other a/v ever on system.
I’ve heard that Comcast did have a major DNS server failure on the east coast recently, that could be part of the problem.
http://www.engadget.com/2010/12/05/comcast-internet-down-in-the-midwest-dns-servers-to-blame-again/
http://www.chicagobreakingnews.com/2010/12/comcast-internet-outage-affecting-chicago.html
As a side note, you could try changing your DNS servers in your router (or just your computer) to fix that problem once and for all.
OpenDNS is a free service that allows you to not only have better DNS lookup times, but it also allows you to control which sites you allow on your network. It’s good to keep the kiddie’s out of bad sites, but can also be used to prevent yourself from accessing harmful websites as well. It’s quite useful.
Check them out here: http://www.opendns.com
Instructions can be found here: http://www.opendns.com/support/videos/