It's called "hyper-targeting", and it's what cookies are for.

Every move you make on the Web is scrutinized by trend-analysis software designed to place advertising in front if you at every possible moment.

When you start to get the feeling that you're a poor, dumb beast to be shorn and milked at will by dozens if not hundreds of commercial entities whose identities are a complete mystery to you, the actual state or affairs will be clear to you.