An anonymous reader's ex-boyfriend has been posting sexually-explicit personal ads on Craigslist, using her name. How can she stop him?

The first thing you should do is contact the web site with the illicit postings. In this case that's Craigslist, which maintains an abuse page in their Help section. A spokesperson assured me that "In most cases, we're able to resolve issues within a very short period of time, often less than an hour."

(I should mention that, six days after I passed on the spokesperson's request that the victim contact him directly, and after I'd already written the first draft of this post, she told me that the contact "asked a few questions but then never replied to my answers.")

But there's a limit to what a site like Craigslist can do. They can't arrest anyone, nor can they legally release incriminating evidence without some form of permission from a court. "To get IP addresses, a subpoena is generally good enough," advises attorney Paul Moretti, a specialist in the field. "To get personal information, you need a search warrant." But Moretti points out that services like Craigslist "work hand-in-hand with law enforcement" and can help walk you through putting together a case.

Whether the company helps you or not, going to your local police force is always a good idea. "Most big city police departments have specific units devoted to cybercrime," Moretti told me. You probably won't find a properly trained and equipped unit if you live in a small town, but your chances of getting solid evidence is considerably greater if you have a good idea who's doing the dirty work.

But you're really in luck (if that word can be applied to stalking victims) if the perp has moved to another state. Then the FBI can get involved. According to Moretti, they might go so far as to seize the suspect's computer to do a forensic search.

What does your ex have to look forward to? "Under federal law," says Moretti, "I believe it's 5 to 10 years in prison, plus a $250,000 fine. Most states have similar criminal law."

What else can you do? You "might notify the ex's ISP," suggests author, attorney, and former PC World columnist Mark Grossman. Such behavior almost always violates the terms of service. Grossman maintains a page about cyberstalking at his Web site.

But, of course, "the big hammer is to sue him," says Grossman. "It sounds great until you realize that it will cost thousands and thousands of dollars," takes years, and does not come with guaranteed results.

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