Facebook vows to fix a flaw in data privacy

When you sign up for Facebook, you enter into a bargain. You share personal information with the site, and Facebook agrees to obey your wishes when it comes to who can see what you post.

At the same time, you agree that Facebook can use that data to decide what ads to show you.

It is a complicated deal that many people enter into without perhaps fully understanding what will happen to their information. It also involves some trust -- which is why any hint that Facebook may not be holding up its end of the bargain is sure to kick up plenty of controversy.

The latest challenge to that trust came on Monday, when Facebook acknowledged that some applications on its site, including the popular game FarmVille, had improperly shared identifying information about users, and in some cases their friends, with advertisers and Web tracking companies. The company said it was talking to application developers about how they handled personal information, and was looking at ways to prevent this from happening again.

Facebook's acknowledgment came in response to an article in The Wall Street Journal that said several popular applications were passing a piece of data known as a user ID to outside companies, in violation of Facebook's privacy policy.

Having a user ID allows someone to look up that user's name and any data posted on that person's public profile, like a college or favorite movies, but not information that the user had set to be visible only to friends.

Privacy advocates and technology experts were split on the significance of the issue.