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Spam isn’t just for your PC anymore. It’s rapidly infecting text messaging, too, which means unsolicited ads for refinancing, discount drugs, and pornography can follow you anywhere you take your mobile phone-and even cost you money, if your carrier charges by the message.

The volume of spam text messages originating from the Internet in North America last year actually exceeded that of legitimate messages, according to Wireless Services of Bellevue, WA. Following the lead of Japan, South Korea, and the European Union, California has passed a law aimed at slowing such messages, and in December the U.S. Congress, as part of the CAN-SPAM Act of 2003, directed the Federal Communications Commission to come up with rules protecting cell-phone users nationwide from unsolicited text messages. But wireless companies and software vendors, worried that mobile spam will deter cell-phone users from subscribing to next-generation data services, aren’t waiting for new regulations before enacting their own measures to stem the tide. Otherwise, the value of these services will be “completely obliterated,” says Jim Manis, president of the Mobile Marketing Association, a trade group focused on the medium.

In November, Wireless Services-one of three companies that handle the text messages sent between the networks of U.S. wireless carriers like Verizon Wireless and SprintPCS-rolled out software that builds on some of the most popular techniques for blocking e-mail spam. “We were getting pressed by our customers to do something,” says Eric Lofdahl, the company’s director of product management.

The technology starts with Bayesian filtering, which spots spam based on its resemblance to messages in a large database of previously identified spam. But it adds a quarantine system. “Maybe there’s a URL that the spammer wants somebody to hit,” Lofdahl explains. “We’ll count how many messages transit our system that have that URL in them over a certain time frame, and if that number exceeds a threshold, we will start diverting those messages into a quarantine area for somebody to look at.” When legitimate messages get quarantined, the company’s spam spotters usually release them within minutes, Lofdahl says.

The company is working to make its spam filters customizable, so that cell-phone owners can decide which messages to accept rather than depend on the carriers’ standards. Right now, says Lofdahl, “If you really are in the market for debt refinancing, you probably aren’t going to get many of the messages you want sent to your cell phone about that.” The company’s improved software, being implemented this year, would let you unblock messages containing certain keywords, such as “debt” or “mortgage.”

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