The Electronic Frontier Foundation revealed this week that the FBI and other federal agencies work undercover on Facebook, Twitter and other social networking sites to shadow suspects and gather evidence in crime investigations.

According to the Associated Press, Freedom of Information Act requests from the California-based EFF netted documents that confirm feds are posing as “friends” and linking up with otherwise ordinary citizens on Facebook and other sites in order to gather background that would discount alibis in crime probes and help them locate suspects on the run.

But is it legal? The AP mentions the Los Angeles case in which federal prosecutors unsuccessfully moved against a woman, Lori Drew, for posing as a teen boy on MySpace and then allegedly harassing a 13-year-old neighborhood girl who later hanged herself. She was nabbed for allegedly violating MySpace's terms of service — posing as someone she isn't — and convicted in L.A. before a higher-court judge overturned the ruling.

Aren't federal poseurs on Facebook doing the same thing Drew did? Facebook has a similar rule against giving false information when opening an account on the site.

Former U.S. cybersecurity prosecutor Marc Zwillinger argued that investigators should be able to go undercover in cyber-world just as they do on the street. Federal authorities said they have tracked down fugitives by linking up with their friends on Facebook.

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