Many of the most popular applications, or "apps," on the social-networking site Facebook Inc. 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, a Wall Street Journal investigation has found.
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.
The problem has ties to the growing field of companies that build detailed databases on people in order to track them online—a practice the Journal has been examining in its What They Know series. 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.
"Apps" are pieces of software that let Facebook's 500 million users play games or share common interests with one another. The Journal found that all of the 10 most popular apps on Facebook were transmitting users' IDs to outside companies.
The apps, ranked by research company Inside Network Inc. (based on monthly users), include Zynga Game Network Inc.'s FarmVille, with 59 million users, and Texas HoldEm Poker and FrontierVille. Three of the top 10 apps, including FarmVille, also have been transmitting personal information about a user's friends to outside companies.
Most apps aren't made by Facebook, but by independent software developers. Several apps became unavailable to Facebook users after the Journal informed Facebook that the apps were transmitting personal information; the specific reason for their unavailability remains unclear.
The information being transmitted is one of Facebook's basic building blocks: the unique "Facebook ID" number assigned to every user on the site. Since a Facebook user ID is a public part of any Facebook profile, anyone can use an ID number to look up a person's name, using a standard Web browser, even if that person has set all of his or her Facebook information to be private. For other users, the Facebook ID reveals information they have set to share with "everyone," including age, residence, occupation and photos.
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.
Defenders of online tracking argue that this kind of surveillance is benign because it is conducted anonymously. In this case, however, the Journal found that one data-gathering firm, RapLeaf Inc., had linked Facebook user ID information obtained from apps to its own database of Internet users, which it sells. RapLeaf also transmitted the Facebook IDs it obtained to a dozen other firms, the Journal found.