A group of hackers claims to have completely cracked T-Mobile's network in the US, and stolen proprietary operating data, customer databases and financial records.

A message posted on the Full Disclosure mailing list said that the hackers have emailed T-Mobile's rivals with an offer to sell the information, but that they had not heard back. They are now offering it to the highest bidder.

"We have everything, their databases, confidential documents, scripts and programs from their servers, financial documents up to 2009," said the posting.

"We already contacted their competitors and they didn't show interest in buying their data - probably because the mails got to the wrong people - so now we are offering them for the highest bidder. Please only serious offers, don't waste our time."

To substantiate the claims, the hackers posted material on the site which they claim came from T-Mobile's servers, although opinion is divided about its authenticity.

In the past such an offer would be highly unlikely, since it automatically draws the attention of law enforcement. Nevertheless, T-Mobile has said that it is investigating the claims.

"The protection of our customers' information, and the safety and security of our systems, is absolutely paramount at T-Mobile," said the company in a 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."