WASHINGTON (AP) - U.S. law enforcement agents are following the rest of the Internet world into popular social-networking services, going undercover with false online profiles to communicate with suspects and gather private information, according to an internal Justice Department document that offers a tantalizing glimpse of issues related to privacy and crime-fighting. Think you know who's behind that "friend" request? Think again. Your new "friend" just might be the FBI. The document, obtained in a Freedom of Information Act lawsuit, makes clear that U.S. agents are already logging on surreptitiously to exchange messages with suspects, identify a target's friends or...