In the heartbeat between clicking a link and the page appearing, an auction happens: data about you is broadcast, advertisers bid for your eyeballs, the highest wins, and their ad loads — in about 0.2 seconds. It runs on almost every page you open. Here it is, slowed down 1000×. Set your profile, then load the page.
That’s real-time bidding (RTB), the engine of online advertising. The moment a page starts to load, a “bid request” carrying data about you — your location, device, a tracking ID, and inferred interests — is blasted to dozens or hundreds of companies. They bid in a split-second auction; the winner’s ad appears. It’s real, it’s constant, and two things sting: companies that lose the auction often still keep your data, and the more sensitive the inference (a health worry, a gambling habit), the more some bidders will pay — including ones who target exactly the people who can least afford it. You are the thing being sold, hundreds of times a day, and your cut is zero.
A teaching model — bidders and numbers are illustrative, but RTB, sensitive-segment targeting, and bid-request data leakage are real. No accounts, no tracking, nothing leaves your device. CC0.