T-Mobile US confirmed hackers had managed to gain access to some of its data, though is still yet to determine what exactly had been gathered as it continues to investigate claims information on 100 million users was being sold online.

In a statement, the operator explained the entry point hackers used had now been closed, with a deep technical review of its systems ongoing to define what was exposed.

Its investigation found “unauthorised access to some T-Mobile data occurred”, but the US operator is yet to determine “there is any personal customer data involved.”

“This investigation will take some time but we are working with the highest degree of urgency,” it added. “Until we have completed this assessment we cannot confirm the reported number of records affected or the validity of statements made by others.”

The probe follows widespread media reports on 15 August claiming hackers were offering a range of personal data purported to have been from T-Mobile servers for sale on an online forum.

Information being offered is claimed to include phone, IMEI and social security numbers, along with names, addresses and driver licence details.