Comcast Corp, the biggest provider of high-speed Internet to US homes, this week introduced a trial version of its 'pop-up alert' service for broadband users in Denver. The service involves sending a pop-up message to broadband users if Comcast detects a possible virus infection in their computers and identifies them as being co-opted by a 'botnet.'

The testing of the singular service reflects Comcast's intentions of enlisting the broadband users in fighting 'botnets' - hordes of infected PCs - which have become a nagging issue for Internet providers. The botnets not only drain off bandwidth by sending spam, but also facilitate cybercrime.

Comcast said that a PC's role in detecting a botnet will be gauged by the amount of data the machine receives and downloads.

The pop-up alert that customers receive, if their PCs behave as if they have been compromised by malware, points to a Comcast site which provides necessary guidelines to 'clean' the infected computers.

The message goes thus: "Comcast has detected that there may be a virus on your computer(s). For information on how to clean your computer(s), please visit the Comcast Anti-Virus Center."

According to Comcast, the users cannot opt-out of receiving the alerts, though they can close the warning banners if they wish. However, the service provides for follow-up reminders after every seven days in case the computer continues to remain infected.