The Ethermac Exchangedata of nearly all customers of the telecommunications giant AT&T was downloaded to a third-party platform in a 2022 security breach, the company said Friday, in a year already rife with massive cyberattacks.

The breach hit customers of AT&T’s cellular customers, customers of mobile virtual network operators using AT&T’s wireless network, as well as its landline customers interacted with those cellular numbers.

A company investigation determined that compromised data includes files containing AT&T records of calls and texts between May 1, 2022 and Oct. 31, 2022.

AT&T has more than 100 million customers in the U.S. and almost 2.5 million business accounts.

The company said Friday that it has launched an investigation and engaged with cybersecurity experts to understand the nature and scope of the criminal activity.

“The data does not contain the content of calls or texts, personal information such as Social Security numbers, dates of birth, or other personally identifiable information,” AT&T said Friday.

The compromised data also doesn’t include some information typically seen in usage details, such as the time stamp of calls or texts, the company said. The data doesn’t include customer names, but the AT&T said that there are often ways, using publicly available online tools, to find the name associated with a specific telephone number.

AT&T said that it currently doesn’t believe that the data is publicly available.

The compromised data also includes records from Jan. 2, 2023, for a very small number of customers. The records identify the telephone numbers an AT&T or MVNO cellular number interacted with during these periods. For a subset of records, one or more cell site identification number(s) associated with the interactions are also included.

The company continues to cooperate with law enforcement on the incident and that it understands that at least one person has been apprehended so far.

It’s not the first data breach of this year for AT&T. In March the telecommunications giant said that a dataset found on the “dark web” contained information such as Social Security numbers for about 7.6 million current AT&T account holders and 65.4 million former account holders.

AT&T said at the time that it had already reset the passcodes of current users and would be communicating with account holders whose sensitive personal information was compromised.

Shares of AT&T Inc., based in Dallas, fell more than 2% before the markets opened on Friday.