Barton Gellman

Stuxnet, a computer worm reportedly developed by the United States and Israel that destroyed Iranian nuclear centrifuges in attacks in 2009 and 2010, is often cited as the most dramatic use of a cyber weapon.

Every time you log in to Facebook, every time you click on your News Feed, every time you Like a photo, every time you send anything via Messenger, you add another data point to the galaxy they already have regarding you and your behavior.