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 email@example.com and firstname.lastname@example.org) 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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