Sure, we all love Doctor Who star David Tennant. He's our time-traveling, swashbuckling hero, and we all would do anything for him. But if he tells you the future of the time-space continuum depends on you giving him your personal information, make sure you're dealing with the real David first. Apparently somebody (or somebodies) is/are pretending to be Tennant on message boards, MySpace, Facebook and other social networking sites, and trying to use that bit of identity theft to enable other bits of identity theft. And possibly to lure people into going some place to meet the Barty Crouch Jr. actor himself.
But don't take my word for it. Here's a David Tennant lookalike to provide more dire warnings: