You've got porn!
The AP astounds with Suspected Porn Site Burglar Arrested:

GILLETTE, Wyo. -- The case of the mystery porn downloader may have been solved.

A 17-year-old Gillette, Wyo., boy has been arrested on suspicion of breaking into homes and using computers to access pornography on the Internet.
...
Police said one victim discovered nearly $671 worth of unauthorized charges to her checking account, all of which were for companies handling transactions for pornography Web sites.

The alleged victim told police that "she keeps her bank statements on or around the computer desk, and that her checking account information is in a Quicken software program on the computer," the arrest affidavit states.
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Another victim wound up with $164 worth of long-distance charges because an autodialing program had apparently been downloaded, telling the computer to regularly call phone numbers in Africa and Germany, according to police
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"These particular people had their passwords saved, so you just click on an icon and dial in," said Dave Adsit, the Police Department's technology and computer crime manager. "Then when (the suspect) was in there he would go onto pornographic sites and fill out a membership form using a stolen checking account number for payment."

In some cases, the suspect returned to a home repeatedly to use the computer.

Other victims became aware after seeing pornographic material displayed on their Internet browsers, he said.

Some sites will "change a lot of your browser settings, automatically go to the porn sites, make it a home page," Adsit said.

Yeah, that would tend to make you suspicious.