Julia Angwin

In Dragnet Nation, Julia Angwin describes an oppressive blanket of electronic data surveillance. "There's a price you pay for living in the modern world," she says. "You have to share your data."

Nearly all of the most commonly visited websites install invisible tracking software on your computer so the information can be sold to advertisers. Julia Angwin, who recently led a team of Wall Street Journal reporters investigating the practice, explains what companies do with the information -- and how you can protect your privacy online.