An unknown person on Saturday claimed to have obtained confidential T-Mobile data and offered to sell the information.

"Like Checkpoint, T-Mobile has been owned for some time," says a note posted to the Full Disclosure mailing list. "We have everything, their databases, confidential documents, scripts and programs from their servers, financial documents up to 2009."

The "Checkpoint" mentioned in the note appears to be a reference to alleged vulnerabilities in security hardware from Check Point Software Technologies. A company official did not immediately respond to a request for comment.

The note continues, stating that because competitors haven't responded to an offer to sell the T-Mobile data, the data is now available to the highest bidder.

As proof, the note includes a data dump of information that appears to pertain to corporate operations, though the data listed isn't sensitive in any way or worth anything as shown.

There is some reason to doubt the authenticity of the note. The e-mail address listed, [email protected], is not currently an active account. It may have been active and been shut down at the request of law enforcement authorities. Or it may never have been active. According to the Safe-mail Web site, "Fraudsters and spammers often claim to be sending messages from our system, when they are in fact using another system."

Safe-mail didn't respond to a request for comment.

Mary Landesman, senior security researcher at ScanSafe, suggests, however, that the sample data isn't likely to be fabricated. "Regarding the truth of the claim, there is an extremely long list of source locations and IP addresses involved," she said in an e-mail. "This is indicative of a serious attack. It is unlikely that 'fakers' would go through all of the trouble."

Were the note merely an attempt to damage T-Mobile's reputation and possibly affect its stock price, one would expect T-Mobile to issue a statement denying the unknown person's claim. T-Mobile, however, says it's still looking into the matter. "The protection of our customers' information, and the safety and security of our systems, is absolutely paramount at T-Mobile," the company said in an e-mailed statement. "Regarding the recent claim, we are fully investigating the matter. As is our standard practice, if there is any evidence that customer information has been compromised, we would inform those affected as soon as possible."

On Monday evening, a T-Mobile spokesperson issued a revised statement, via e-mail, acknowledging that a data breach had occurred and implying that no personally identifiable information appears to have been compromised.

"To reaffirm, the protection of our customers' information and the security of our systems is paramount at T-Mobile. Regarding the recent claim on a Web site, we've identified the document from which information was copied, and believe possession of this alone is not enough to cause harm to our customers.

We continue to investigate the matter, and have taken additional precautionary measures to further ensure our customers' information and our systems are protected. At this moment, we are unable to disclose additional information in order to protect the integrity of the investigation, but customers can be assured if there is any evidence that customer information has been compromised, we would inform those affected as quickly as possible."

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