The same law that allows the RIAA to find out who is illegally sharing Johnny Cash tunes also lets anyone--including abusive spouses, online stalkers, and blackmailers--find out personal information (perfectly legally in many cases) about people that they've corresponded with on the Internet.

The Digital Millennium Copyright Act (DMCA) allows copyright holders to seek damages from anyone who steals copyrighted material. But the RIAA by itself can't get the names of the file-sharers. The organization only knows the file sharer's IP address at the time of the alleged violation.

Using those two pieces of information, however, the RIAA can file a form with a federal court clerk, and have the clerk issue a subpoena--a legal demand for information from the suspected music pirate's ISP--to find out the name, mailing address, phone number, and e-mail address of the copyright violator.

The problem is that you can do the same thing. Thanks to section 512(h) of the DMCA, literally anyone can walk into a federal courthouse, fill out a form alleging that they're the victim of a copyright violation, and walk out with a legal document in hand that gives them the right to ask an ISP for a customer's contact information.

The law requires only that you have a "good faith belief that someone violated your copyright," says Sarah Deutsch, vice president and associate general counsel for Verizon, one of the ISPs fighting the RIAA's subpoenas against Internet users. No judge reviews the request, and the clerk issues the subpoena on the spot.

And in fact someone could technically argue that an online acquaintance has violated their copyright. "Every e-mail you write is copyrighted automatically," says Wendy Seltzer, staff attorney for the Electronic Frontier Foundation. "As soon as you fix something in a tangible medium of expression, including when you type it into a computer, it's copyrighted." So an enemy could claim that you forwarded their e-mail message without their permission and thus violated their copyright.

"Until recently, you had to file a lawsuit and go before a judge [to get a subpoena], so it was much less likely the process would be abused," Deutsch said, adding that, even under the USA Patriot Act, law enforcement has to jump through more hoops to get the same data about a suspected terrorist than the RIAA does to find out about a file swapper.

No matter which side of the file-sharing debate you find yourself on, there's no denying that the ease with which anyone can get a subpoena without judicial scrutiny creates alarming potential for abuse.

Andrew Brandt is senior associate editor for PC World. E-mail him at privacywatch@pcworld.com. You can find more Privacy Watch columns here.