AT&T Informs 9 Million Customers of Data Breach

AT&T has informed nearly 9 million customers that their information was compromised after a marketing vendor was hacked in January. The company has issued a breach notification that reveals that Customer Proprietary Network Information (CPNI) was exposed.

The data breach notification did not disclose the number of customers impacted, but AT&T told BleepingComputer that “approximately 9 million wireless accounts had their Customer Proprietary Network Information accessed.”

The CPNI data that was breached includes first names, wireless account numbers, wireless phone numbers, and email addresses. In some cases, impacted customers had their rate plan names, monthly payment amounts, past due amounts, minutes used, and various monthly charges exposed, although this information was several years old.

Thankfully, sensitive personal information like social security numbers, account passwords, or credit card details were not obtained by the hacker.

AT&T clarified that the vendor security incident did not compromise its systems, and the disclosed data was mainly associated with device upgrade eligibility. The company has duly notified federal law enforcement about the unauthorized access to customer data, as mandated by the Federal Communications Commission.

All AT&T customers have been advised to toggle off CPNI data sharing on their accounts. This can be done by making a CPNI Restriction Request, which should help reduce exposure risks from future third-party vendor hacks.

AT&T has not yet provided any information on which third-party vendor was breached for this data to be disclosed.

T-Mobile also disclosed a data breach this month that affected over 39 million of its customers. Similar to AT&T, the hacker didn’t gain this information by breaching T-Mobile’s internal systems. Instead, a vulnerability in an Application Programming Interface (API), was exploited by a threat actor for over a month before being detected and fixed by T-Mobile.