Comcast to warn infected users with pop-up

For instance, a significant overnight spike in traffic being sent from a particular Internet Protocol address could signal that a computer is infected with a virus taking control of the system and using it to send spam as part of a botnet.

The alerts are triggered "when we see computers on our network that are doing things that are known bot activities--say, a computer is spewing out thousands of spam e-mails," said Jay Opperman, senior director of security and privacy at Comcast.