• by Wendy Davis , Staff Writer @wendyndavis, November 11, 2011

When Mark Zuckerberg appeared on the “Charlie Rose” show this week, the Facebook CEO insisted that the social networking service was more transparent about privacy issues than Google, Yahoo or any other companies that ran big ad networks. That's because, according to Zuckerberg, those companies collect data behind the scenes, tracking users as they surf the Web in order to serve them ads.

In fact, Facebook has often said that it doesn't track users as they surf the Web in order to serve them targeted ads. Turns out, however, that the company recently applied for a patent to do just that.

News of the patent -- which describes a method of tracking users throughout the Web and serving them tailored ads -- was first reported by Michael Arrington on his blog, Uncrunched.

Facebook spokesperson Andrew Noyes says the patent centers on the company's social plugins, and not the tracking of logged-out users.

As for the part about serving ads to users based on the sites they visit, Noyes says that “technology companies patent lots of ideas.”

He adds: “Some of these ideas become products or features and some don’t. As a result, current functionality and future business plans shouldn’t be inferred from our patent applications.”

But some lawmakers want more details. Reps. Ed Markey and Joe Barton, co-chairs of a bipartisan House caucus on privacy, this week posed additional questions to Zuckerberg. “We understand that there are a variety of motivations to file for a patent beyond protection of already employed or planned practices. Accordingly, it would be fruitful for Facebook to explain why it filed a patent 'for tracking information about the activities of users of a social networking system' while simultaneously stating 'Facebook does not track people across the Internet,' ” they wrote.

The lawmakers are requesting that Zuckerberg answer whether Facebook intends to start tracking users on other sites, even when those users are logged out. Markey and Barton also are asking Facebook how it “intends to integrate the location data of its users into its targeted advertising system.”

Facebook has until Dec. 1 to respond.