US telco AT&T is investigating a dataset released on the dark web about two weeks ago, saying a preliminary analysis shows it has impacted approximately 7.6 million current account holders and 65.4 million former account holders.
The company said the data set appears to be from 2019 or earlier.
AT&T said it does not have evidence of unauthorised access to its systems resulting from the incident.
The company said it is not yet known whether the data originated from AT&T or from one of its vendors.
AT&T said the incident has not had a material impact on its operations, and said the source of the data is still being assessed.
AT&T is in contact with all those impacted and has reset passcodes for 7.6 million current customers. It also said it will offer credit monitoring wherever applicable.
The wireless carrier’s 5G network covers around 290 million people across the United States.
In February, AT&T had an outage that disrupted calls and text messages for thousands of US users and prompted federal investigations.