So YOU're the one distributing porno on the Web...!

More than a thousand unsuspecting Internet users around the world have recently had their computers hijacked by hackers, who computer security experts say are using them for pornographic Web sites.

The hijacked computers, which are chosen by the hackers apparently because they have high-speed connections to the Internet, are secretly loaded with software that makes them send explicit Web pages advertising pornographic sites and offer to sign visitors up as customers.

Unless the owner of the hijacked computer is technologically sophisticated, the activity is likely to go unnoticed. The program, which only briefly downloads the pornographic material to the usurped computer, is invisible to the computer's owner. It apparently does not harm the computer or disturb its operation.

The hackers operating the ring direct traffic to each hijacked computer in their network for a few minutes at a time, quickly rotating through a large number. Some are also used to send spam e-mail messages to boost traffic to the sites.

"Here people are sort of involved in the porno business and don't even know it," said Richard M. Smith, an independent computer researcher who first noticed the problem earlier this month. Mr. Smith said he thought the ring could be traced to Russian senders of spam, or unwanted commercial e-mail.

By hiding behind a ring of machines, the senders can cloak their identity while helping to solve one of the biggest problems for purveyors of pornography and spam: getting shut down by Internet service providers who receive complaints about the raunchy material.

The web of front machines hides the identity of the true server computer so "there's no individual computer to shut down," Mr. Smith said. "We're dealing with somebody here who is very clever."

The creators of the ring, whose identities are unknown, are collecting money from the pornographic sites for signing up customers, the security experts say. Many companies play this role in Internet commerce, getting referral fees for driving customers to sites with which they have no other connection.

The ring system could also be used by the hackers to skim off the credit card numbers of the people signing up, said Joe Stewart, senior intrusion analyst with Lurhq, a computer security company based in Myrtle Beach, S.C.

The current version of the ring is not completely anonymous, since the hijacked machines download the pornographic ads from a single Web server. According to the computer investigators, that machine apparently is owned by Everyones Internet, a large independent Internet service company in Houston that also offers Web hosting services to a large number of companies. Jeff Lowenberg, the company's vice president of operations, said that he was not aware of any illegal activity on one of his company's computers but said that he would investigate.


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