A federal prosecutor tracked down a Seattle fraud suspect in Mexico this year through his Facebook posts.

A man's Twitter messages to fellow demonstrators at a recent protest in Pittsburgh led to an FBI search of his home and short-lived charges of interfering with police.

The CIA and other U.S. intelligence agencies reportedly are investing in a software firm that monitors half a million social networking Web sites each day.

There's nothing wrong with law enforcement agencies' using Internet technology to investigate crimes, Bay Area privacy advocates say. But they want the federal government to say how, when and why its agents look at Americans' social networking accounts.

"These are new tools. There hasn't been a lot of discussion about how law enforcement can use them and what's appropriate, what's ethical," said attorney Marcia Hofmann of the Electronic Frontier Foundation, which filed a Freedom of Information Act lawsuit this week against the Defense Department, the Justice Department, the CIA and other federal agencies with intelligence-gathering arms.

The suit, in U.S. District Court in San Francisco, seeks each agency's policies and guidelines on using social networking sites and its safeguards for preventing abuses. The Electronic Frontier Foundation says the government has ignored requests since October to disclose the information voluntarily.

"There are a lot of very appropriate law enforcement uses of social networking sites," said Shane Witnov, a UC Berkeley law student working on the case for the school's Samuelson Law, Technology and Public Policy Clinic. But, he said, "The American people have a right to know if they're being surveilled."

Hofmann said what is known about police using interactive Web sites to nab suspects comes from media accounts. She said there are few court records or laws that directly address such surveillance.

Public or private?

Federal and state laws require police to get a warrant before reading the contents of a private e-mail. But it's not clear when, or whether, a widely shared networking site is considered private, Hofmann said.

She said Facebook users might be entitled to privacy protection when they limit access to their communications to people they designate as friends.

Media reports from several cities have described police posing as friends to enter accounts. Although officers in conventional investigations commonly work undercover, Hofmann said, creating a false profile to gain access to private, online information might violate federal laws on electronic surveillance.

At the least, she said, it "presents a lot of ethical concerns."

Occasionally, officers have no need to resort to such subterfuges to find incriminating information online.

Boasting on Facebook

One notable case involved Maxi Sopo, who was wanted on bank fraud charges in Seattle and posted messages on Facebook reveling in his life of ease in Mexico.

Sopo's Facebook page was private but his list of friends was public, and included a former Justice Department employee whose name was spotted by a federal prosecutor in Seattle, authorities said. The man, who had no idea Sopo was wanted, provided information that enabled Mexican police to arrest him in September.

One controversial case involved allegations of criminal misuse of electronic networking.

Elliot Madison, a protester at the Group of 20 economic summit in Pittsburgh, was arrested by state police in September in a hotel where he was sending Twitter messages to demonstrators. His lawyer said Madison had simply been telling them that police were ordering them to disperse.

Madison was booked on suspicion of interfering with legal arrests - an apparently unprecedented charge that prosecutors eventually decided not to pursue.

Madison said the FBI later raided his New York City home and handcuffed him while agents ransacked the premises, a search that produced no charges. It all happened, he noted, while the U.S. government was praising dissidents in Iran who used Twitter to communicate with each other and the outside world.

Keeping tabs

The government, meanwhile, is reportedly teaming up with the private sector to monitor public sites such as Twitter and YouTube. Wired.com reported in October that In-Q-Tel, the investment arm of the CIA and other intelligence agencies, was investing in Visible Technologies, a software company that keeps tabs on more than half a million Web sites, blogs and online forums each day.

Witnov, the Berkeley law student, is the co-author of one of the few published sets of guidelines for lawyers' use of social networking sites.

Adopted last year by the Santa Clara County public defender's office, the handbook says browsing a consenting person's Web site is acceptable. Misrepresenting an employer or job title is discouraged, it says, and creating fake accounts or contacting a witness without identifying one's self is off-limits.

The elusive goal, Witnov said, is the proper balance between "what we as a society want to protect ourselves from criminals and to protect ourselves from invasion of privacy."