T-Mobile Says 6 Million More Customer Files Accessed in Data Breach


T-Mobile US Inc. said the hack of its user database exposed another 6 million customers’ details, bringing the total number of compromised user records to more than 54 million as the carrier continues to investigate the extent of the intrusion.

In an update Friday, the company said 5.3 million more current T-Mobile customers had their names, addresses, birth dates and phone numbers exposed, though their Social Security numbers or driver’s license details weren’t included. The company also identified another 667,000 former clients who had some personal information compromised.

T-Mobile also said the hack accessed IMEI and IMSI data—serial numbers tied to phones—from current customers. These phone records were taken from the 5.3 million customers as well as 7.8 million customers that T-Mobile had identified as victims earlier this week.

Security researchers said the phone-specific serial numbers, when paired with other personal information, could prove particularly damaging in the hands of criminals who use the data to commit fraud. Attackers with information about a person’s subscriber identity module, or SIM, can use the information to impersonate a victim and take over his or her phone line.

“Our investigation is ongoing and will continue for some time, but at this point, we are confident that we have closed off the access and egress points the bad actor used in the attack,” the company said

T-Mobile opened an online portal with information for potential victims and said it would offer two years of free identity-protection services from security firm McAfee.

On Monday, T-Mobile said it had learned that an individual in an online forum claimed to have breached its systems and was attempting to sell stolen customer data. The company said early Wednesday that attackers made off with personal data from more than 40 million people, including former and prospective customers.

Separately, AT&T Inc. denied a claim by a hacker group offering to sell records on more than 70 million of its customers on the same website where some T-Mobile data was previously offered for sale.

“Based on our investigation today, information that appeared in an internet chat room does not appear to have come from our systems,” AT&T said.