try this »amibotted.comcast.net/all-clear. ··· ear.html
If it shows a problem, and you are SURE (actually scanned with multiple products, not just assume Mac's are immune ) that you are clean, it means ComCast has detected a bot like pattern (either excessive bursts of mass emails steady trickles of packets to and from known bad addresses)
You will need to figure out what and how to stop it.
BTW Mac's are not and never have been immune (particularly since going toward more main stream *nix type O/Ss and now have enough market share/horsepower to be worth writing exploits for (like in high school, being popular can be a path new and unpleasant diseases
) time to use protection