DavidR
4
Avast has nothing to do with being unable to connect to windows update, it isn’t a firewall and it would be treated in the same way as any other HTTP web site.
This could well be an indication that your HOSTS file might have been modified.
– HOSTS file redirect a common malware tactic to block AV sites making it difficult to remove malware - 127.0.0.1 check your HOSTS file using notepad or a text editor of your choice, C:\WINDOWS\system32\drivers\etc\hosts or do a search for HOSTS to find it if not there.
Once open you are looking for entries windows update or security sites like avast.com on the line, you may well see other AV sites, post the contents of the hosts file. http://en.wikipedia.org/wiki/Hosts_file