Antivirus specialist Sophos has launched a "ZombieAlert service" that promises to find unsolicited e-mail messages originating from computers being used as spam relays. Using "spam traps" that are configured so they are unlikely to receive legitimate messages, the service will inform ZombieAlert subscribers if their systems are being used.

"We endeavor to ensure that of the e-mails that enter the spam trap, there is a statistically insignificant amount of real e-mail. Everything coming in is not supposed to be there," said Paul Ducklin, head of technology at Sophos Asia-Pacific.

"The obvious early adopters will be environments like universities and ISPs, who have huge amounts of Internet traffic--diverse populations that are not necessarily centrally regulated," Ducklin said.