Connect the dots
It’s not just applications inside of Facebook that pass information about you. Through a program called Connect, applications outside of Facebook exchange information with the social network. Hundreds of websites and mobile applications connect you to Facebook and share your activities with your friends—and with advertisers.
Everything you do on or through Facebook is another piece of information companies use to profile you. Every piece of information you give them is one more thing they use to target ads. Facebook works because we tell it everything there is to know about us.