I can't say I know much about their warning system, short of an article I read by Brian Krebs when Comcast first announced the program. See Comcast Pushes Bot Alert Program Nationwide.
Did you run any scans?
According to one forum, Comcast provides a link for their customers to check where the suspicious activity is coming from. See Am I Botted?
As I stated, I'm not familiar with the program. The Comcast Forum has quite a few threads on the topic. (See these )
If you don't get any further help here, you might want to consider posting there. But.. if you haven't run any scans, I would consider it the first order of business.
It's the best I know to suggest..
Comcast warns me that I may have a bot on my pc.
How can I detect and remove it?