The “Man”
The government just loves Facebook. Criminals tend not to be very bright people, and it turns out some of them love to brag about their crimes. You or I, having just robbed a bank or killed a guy, would be smart enough to keep it to ourselves. That’s why you and I have jobs that don’t involve ski masks and gunplay. (Unless you’re a professional biathlete, in which case, good for you.)
The FBI, Homeland Security, and the INS have created false profiles and friended their suspects. Are you sure that’s your grandma who just friended you? If you work on Wall Street, it might actually be the Secret Service, checking to see if you’re posting any “special” accounting tips or vacation photos from the Cayman Islands.