"No company should track customers without their knowledge or consent, especially a company with 800 million users and a trove of unique personal data on its users," Rockefeller said in a statement. "If Facebook or any other company is falsely leading people to believe that they can log out of the site and not be tracked, that is alarming."
Facebook has acknowledged that it collects some data from users even after they log out of their accounts. For example, the company is notified when users visit websites that feature its "Like" button, even if the users are not signed in.
Facebook spokesman Andrew Noyes said that Facebook deletes account-specific cookies, or tracking files, when a person logs out of their account. The cookies that remain on a person's computer are used for safety and protection, such as identifying spammers or helping users log back into their account if it has been hacked, he said. He emphasized that Facebook does not sell its users' information to third parties.
Rockefeller did not announce a date for the hearing or a list of witnesses, but he said he will "invite Facebook and others to explain how they are using personal information."
The Federal Trade Commission and Facebook are reportedly near a settlement over charges stemming from changes Facebook made to its privacy settings in 2009. The social network made parts of users' profiles public by default, including their picture, city and friend list. Users did not have to agree to the changes before they were implemented.