EDIT: about the guy who said Norton comes free ...
http://customer.comcast.com/help-and-support/internet/downloading-the-norton-security-suite
It doesn't come with any bloat crap from them does it?
I installed this a while back for a small business that insisted that they wanted to manage their own AV, although we offer several cloud-based MSP's at some ridiculous savings. Didn't seem to be much bloat, think there's some optimization tools that will run automatically if you don't disable them