CREEPY: Facebook Figured Out My Family Secrets, And It Won’t Tell Me How.

The People You May Know feature is notorious for its uncanny ability to recognize who you associate with in real life. It has mystified and disconcerted Facebook users by showing them an old boss, a one-night-stand, or someone they just ran into on the street.

These friend suggestions go far beyond mundane linking of schoolmates or colleagues. Over the years, I’d been told many weird stories about them, such as when a psychiatrist told me that her patients were being recommended to one another, indirectly outing their medical issues.

What makes the results so unsettling is the range of data sources—location information, activity on other apps, facial recognition on photographs—that Facebook has at its disposal to cross-check its users against one another, in the hopes of keeping them more deeply attached to the site. People generally are aware that Facebook is keeping tabs on who they are and how they use the network, but the depth and persistence of that monitoring is hard to grasp. And People You May Know, or “PYMK” in the company’s internal shorthand, is a black box.

Would you hand the White House keys to someone with that much data on everyone?