It began as a college directory. Two decades later, Facebook holds one of the most detailed records of human behavior ever assembled — who you know, where you go, what you're drawn to, and what you're likely to do next. The company insists it isn't listening through your microphone. But it’s not fighting the rest: invisible pixels that follow you across sites, a location trail it can reconstruct even after you switch tracking off, and data gathered on people who never signed up for an account at all.