The service, called 'Comcast Constant Guard', will alert customers in Denver if Comcast has reason to believe that their home computer has been infected with malware.
Customers will be alerted using a service notice that appears directly in their web browsers, with a direct link to the ISP's anti-virus center, Comcast said. There, they can take steps to diagnose and remediate the malware problem.
"We are among the very first ISPs in the US to take this kind of proactive approach to help protect customers online", the company said in a blog entry.
The service has two other components. High-speed internet customers can already download the McAfee Internet Security Suite, which Comcast provides for free, along with a toolbar that includes spyware detection and removal, and a pop-up ad blocker with built-in anti-phishing software. Comcast is also rolling its Security Channel, an online security advisory and education service, into the Constant Guard brand.
Security advocates have been calling on ISPs to take a more proactive stance when it comes to stopping malware, and the spam that helped to distribute it. Some ISPs have begun blocking port 25 to stop malware acting as an SMTP server and sending its own email.