According to a Wall Street Journal investigation, a significant number of the most popular Facebook "apps" (applications) have been transmitting your personal information to dozens of advertising and Internet tracking companies. They're also grabbing information about all your friends — who they are, what they do, where they go online.
This problem affects tens of millions of people who use Facebook's apps, even if you set your Facebook profile to the utmost privacy.
Tracking people online is a huge business, and lots of companies are making a killing building detailed databases on people so that they can track their online comings and goings. They then sell these data to advertisers. It's a multibillion-dollar business, and you got involved when you willingly put any of a dozen apps on your Facebook page.
One of the questions, of course, is "how long has this been going on?" As of this writing, we don't know...