Some 73 million current and former AT&T customers had personal information including Social Security numbers leaked onto the dark web earlier this month, the company said Saturday.
"While AT&T has made this determination, it is not yet known whether the data in those fields originated from AT&T or one of its vendors," the company said in a statement.
"With respect to the balance of the data set, which includes personal information such as social security numbers, the source of the data is still being assessed," it said.
According to a preliminary examination, the data leak appears to be from 2019 and affects about 7.6 million current customers and about 65.4 former account holders, the company said.
AT&T said it has no evidence of "unauthorized access" to its systems.
It recommended current and former customers to change their passwords, and said it will offer credit monitoring "where applicable" to those affected.
The data leak has had no "material impact" on its operations, the company said.
AT&T was hit with an outage in February that affected its approximately 240 million subscribers. It offered customers a $5 credit.
