AT&T Awarded Patent for Filter Evasion Method

AT&T has been awarded a patent on a common technique used by spammers to evade spam filters.

Filed in 1999, patent number 6,643,686 describes “a method for counteracting a filtering technique based upon the detection of a duplicate.”

That method, which AT&T Labs claims to have developed, trumps the common spam filtering technique of blocking mail based on the detection of duplicate messages. It does that by changing each message slightly as it goes out, so the messages aren’t exactly duplicates.

The now-patented method, a common weapon in spammers’ arsenal, can be carried out through a variety of means, including by adding random characters to an email’s body or subject line, thereby reducing the chance a filtering system will identify a match between two or more duplicate messages and block them.

AT&T said it does not intend to use its patented technique to evade spam filters.

“AT&T is making every effort to stop spam, not encourage it,” said Michael Dickman, a spokesperson for AT&T Labs. “This patent is an innovative approach in the arsenal of tools open to AT&T to try to discourage spam.”

By patenting the method, AT&T could theoretically forbid spammers from using it to improve delivery of unsolicited email, a tactic Dickman hinted the company is considering. Whether that could prevent spammers from using the method or win AT&T sizeable patent infringement awards is unlikely, however, since few spammers or fraudulent mailers have been successfully prosecuted under existing state and federal laws.

The slim likelihood that AT&T might successfully sue spammers for patent infringement led one SlashDot discussion member to sardonically suggest a patent on bank robbery as a solution to that crime.

However, SpamCon Foundation Executive Director Andrew Barrett said the methods for pursuing a patent lawsuit are better tested than anti-spam statues, and AT&T may be able to succeed in prosecuting some well-known spammers with significant assets.

“The patent could potentially be an effective tool against spam, depending on how broad the claims within it can be interpreted,” Barrett said. “It’s a bit like trying to convict Al Capone for tax evasion, but if it makes a dent in the flow of spam, no one will care.”

Dickman said AT&T is still evaluating the implications of its patent and keeping its options open.

“[Inventor Robert Hall] recognized back in 1999 that a spammer might defeat a filter by foiling its recognition method,” he said. “So he filed a patent. What could be done with it is an open-ended question.”

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