Danny,
I've installed it on 3 computers with a router. They ask you for your comcast mail address and password in order to install.
Also, I use ccleaner to help clean up the harddrive. It does wonders for your performance.
http://www.filehippo.com/download_ccleaner/
I also notice file hippo has the other freeware anti virus being bandied about in this thread.
Mark