T-Mobile US reportedly began an investigation into claims data stolen from its servers was being offered for sale on an online forum, with the information said to relate to more than 100 million people.

Reuters reported the operator was looking into the validity of claims, which were reported by multiple technology websites in the US.

Motherboard, a technology news service owned by Vice, noted the hackers were selling phone, IMEI and social security numbers, along with names, addresses and driver licence details all allegedly obtained from the operator’s servers.

The hackers apparently have now lost access to the compromised infrastructure, the news website reported, but claim to have already backed-up the information in a number of locations.

T-Mobile has been the victim of several breaches over the years, with the company informing some customers in January of its most recent confirmed security incident.

In its letter to users at the time, it noted this incident only covered limited data such as phone numbers, number of lines subscribed to and in some cases call-related information.