Booby-trap patent thwarts spammers

INTELLECTUAL is not a word you'd normally associate with the purveyors of genital enlargement equipment and erectile dysfunction therapies, otherwise known as spammers. But intellectual property lawyers may soon have them on the run. The granting of a US patent last week to telecoms firm AT&T means spammers can now be sued for patent infringement if they try to defeat the anti-spam filters running on mail servers. On the face of it, AT&T's patent- which covers ways to defeat the filters- seems to reveal too much about how spam filters work and how they can be beaten. The firm has been roundly criticised for giving away such information to spammers. But AT&T says its move will benefit internet users in the long run. Spammers flood the internet by bulk-emailing advertisements to many different addresses, often trawled from newsgroups or guessed from known addresses. Over a third of incoming email at New Scientist is now spam.

Anti-spam filters look for duplicate emails that hit an office system en masse, or reach a private email several times over. Duplicates that are detected are automatically deleted and added to a blacklist, or "quarantined" for IT staff to check manually. The US patent office last week granted AT&T a patent for a "system and method for counteracting message filtering" (US 6643686). It details how anti-spam filter systems work and then reveals a clever way to "foil...spam countermeasures based upon duplicate detection schemes". The strategy involves dividing the list of addresses to be spammed into sub-lists, changing the header and message text slightly for each list and juggling the lists so that similar addresses (such as fred1@newscientist.com and fred2@newscientist.com) get messages with different content. But the editor of the Internet Patent News Service newsletter was apoplectic. Greg Aharonian branded the patent "a shining example of corporate R&D irresponsibility" and "a waste of [patent] examiner time". He didn't believe AT&T would enforce the patent and sue spammers who infringe it. "We don't want to say too much and compromise lawsuits," says AT&T spokesman Michael Dickman.

"But contrary to what's being said, this is a legal tool intended as an anti-spam measure. The spammers come at you in every imaginable way. We filed the patent to try and stop them coming this way." There is a precedent for AT&T's "patent and sue" plan. The digital copyright protection firm Macrovision has used the same legal tool to outlaw devices that could defeat copy protection on videotapes and DVDs. Says Macrovision chief William Krepick: "We recognised early on that we would be the target of hackers and circumvention devices and developed a dual-track patenting approach: offensive and defensive. The defensive track was unconventional, since it involved patenting as many ways as we could conceive to defeat our own technology. So we can sue and bring circumvention scofflaws to their knees."

Written by BARRY FOX

New Scientist issue: 29 NOVEMBER 2003

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