The company said it is investigating a data set released on the "dark web" about two weeks ago...
and that its preliminary analysis shows it has impacted approximately 7.6 million current account holders and 65.4 million former account holders.
AT&T said the data set appears to be from 2019 or earlier.
The company said it does not have evidence of unauthorized access to its systems...
and it doesn't know whether the data originated from AT&T or one of its vendors.
AT&T said the incident has not had a material impact on its operations.
The company is in contact with all those affected and has reset passcodes for 7.6 million current customers.
It also said it will offer credit monitoring wherever applicable.
In February, AT&T had an outage that disrupted service for thousands of U.S. users and prompted federal investigations.
