After a week away, there's too much to catch up on - especially the foreclosure mess. If that's on your mind, this Q&A by John Carney of CNBC remains one of the best primers I've seen. And if you're wondering what happens to all those homes that changed hands after foreclosure, take a look at The Finality of Foreclosure Sales, a blog post by University of Illinois law professor Robert Lawless.

But today's most disturbing news is about privacy on Facebook - or the lack thereof - for the social-networking site's 500 million users.  The Wall Street Journal says all 10 of Facebook's most popular apps, including FarmVille and Texas HoldEm Poker, "have been transmitting identifying information—in effect, providing access to people's names and, in some cases, their friends' names—to dozens of advertising and Internet tracking companies."

The story says:

The issue affects tens of millions of Facebook app users, including people who set their profiles to Facebook's strictest privacy settings. The practice breaks Facebook's rules, and renews questions about its ability to keep identifiable information about its users' activities secure. ... It's unclear how long the breach was in place. On Sunday, a Facebook spokesman said it is taking steps to "dramatically limit" the exposure of users' personal information.

"A Facebook user ID may be inadvertently shared by a user's Internet browser or by an application," the spokesman said. Knowledge of an ID "does not permit access to anyone's private information on Facebook," he said, adding that the company would introduce new technology to contain the problem identified by the Journal.

"Our technical systems have always been complemented by strong policy enforcement, and we will continue to rely on both to keep people in control of their information," the Facebook official said.

... The apps reviewed by the Journal were sending Facebook ID numbers to at least 25 advertising and data firms, several of which build profiles of Internet users by tracking their online activities.

The whole story is here, though it requires WSJ subscription access.  It's part of the Journal "What They Know" series about companies that are building detailed databases on people in order to track them online.There's gold in that data, but its existence also challenges some basic consumer expectations about privacy.

Of course, the crucial question here is the cynical one: Is this a Facebook bug or a feature?  The answer will become clearer when we see whether Facebook changes in response.