T-Mobile has admitted that it is the mobile phone carrier recently identified in a Information Commissioner's Office investigation into customer data being illegally sold.

The carrier itself had identified the possible theft of customer records, and a joint investigation was underway, but the Information Commissioner decided to make the information public yesterday.  It is estimated that tens of thousands of users details were sold to rivals and third parties.

In an official statement the company said:

'T-Mobile takes the protection of customer information seriously. When it became apparent that contract renewal information was being passed on to third parties without our knowledge, we alerted the Information Commissioner's Office."

"Working together, we identified the source of the breach which led to the ICO conducting an extensive investigation which we believe will lead to a prosecution. Whilst it is deeply regrettable that customer information has been misappropriated in this way, we have proactively supported the ICO to help stamp out what is a problem for the whole industry. "

The data stolen mainly consisted of customer details and contract end dates - enough for a rival to try to tempt a T-Mobile customer away just before their renewal date, but apparently did not include other personal or payment information. It is thought that the illegal sale of data had been taking place for some time.