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.