Are you a member of Facebook.com? You may have a lifetime contract.

Some users have discovered that it is nearly impossible to remove themselves entirely from Facebook, setting off a fresh round of concern over the popular social network’s use of personal data.

While the Web site offers users the option to deactivate their accounts, Facebook servers keep copies of the information in those accounts indefinitely. Indeed, many users who have contacted Facebook to request that their accounts be deleted have not succeeded in erasing their records from the network.

“It’s like the Hotel California,” said Nipon Das, 34, a director at a biotechnology consulting firm in Manhattan, who tried unsuccessfully to delete his account this fall. “You can check out any time you like, but you can never leave.”

It took Mr. Das about two months and several e-mail exchanges with Facebook’s customer service representatives to erase most of his information from the site, which finally occurred after he sent an e-mail threatening legal action. But even after that, a reporter was able to find Mr. Das’s empty profile on Facebook and successfully sent him an e-mail message through the network.