Just because you mark some of your Facebook data as private doesn't mean that you're hard to track down. Software engineer Reza Moaiandin has learned that it's possible to scoop up the public details of legions of Facebook users simply by guessing phone numbers with a random number generator. You see, the social network defaults to letting anyone search for you using your phone number, even if it's unlisted -- as there's no search limit, all it takes is a script to harvest the user IDs for thousands of people. As you can imagine, there's a real worry that this will not only let black market dealers and hackers collect targets en masse, but help them get numbers to use for phone-oriented attacks and spying.