Selling You on Facebook - WSJ.com

Many popular Facebook apps are obtaining sensitive information about users—and users' friends—so don't be surprised if details about your religious, political and even sexual preferences start popping up in unexpected places. By JULIA ANGWIN and JEREMY SINGER-VINE Apps on Facebook may be grabbing and sharing more personal information than many users realize. And even if people understand that they're sharing personal data, they often can't envision the ways it may be used in the future. WSJ's Julia Angwin explains.Not so long ago, there was a familiar product called software. It was sold in stores, in shrink-wrapped boxes. When you bought it, all that you gave away was your credit card number or a stack of bills.Now there are "apps"—stylish, discrete chunks of software that live online or in your smartphone. To "buy" an app, all you have to do is click a button. Sometimes they cost a few dollars, but many apps are free, at least in monetary terms. You often pay in another way. Apps are gateways, and when you buy an app, there is a strong chance that you are supplying its developers with one of the most coveted commodities in today's economy: personal data.MoreDigits: How to Control What Facebook Apps SeeTesting Facebook Apps: Our MethodologyWhat They Know: A Wall Street Journal Investigation