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 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 threatened legal action. But even after that, a reporter was able to find Das' empty profile on Facebook and successfully sent him an e-mail message through the network.

In response to difficulties faced by ex-Facebook members, a cottage industry of unofficial help pages devoted to escaping Facebook has sprung up online.

"I thought it was kind of strange that they save your information without telling you in a really clear way," said Magnus Wallin, a 26-year-old patent examiner in Stockholm who founded a Facebook group, "How to permanently delete your Facebook account."

The technological hurdles have a business rationale. According to an e-mail message from Amy Sezak, a spokeswoman for Facebook, "Deactivated accounts mean that a user can reactivate at any time, and their information will be available again just as they left it."

But it also means that users cannot disappear from the site without leaving footprints.

Facebook's Web site does not inform departing users that they must delete information from their account in order to close it fully.

Only people who contact Facebook's customer service department are informed that they must painstakingly delete, line by line, all of the profile information, messages and group memberships they may have created within Facebook.

"Users can also have their account completely removed by deleting all of the data associated with their account and then deactivating it," Sezak said in her message. "Users can then write to Facebook to request their account be deleted and their e-mail will be completely erased from the database."