The data 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, as cyberattacks against businesses, schools and health systems continue to spread globally.

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 who interacted with those cellular numbers.

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

"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, or customer names. AT&T, however, said that there are often ways using publicly available online tools to find the name associated with a specific telephone number.

An internal 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 breach.

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.

The year has already been marked by several major data breaches, including an earlier attack on AT&T. In March AT&T 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.

Some auto dealerships are still using pens and paper to close deals after back-to-back cyberattacks last month on a company that supplies them with software. That company, CDK Global, is still attempting to reestablish normal operations.

Alabama's education superintendent said earlier this month that some data was "breached" during a hacking attempt at the Alabama State Department of Education.

Cybersecurity experts are warning that hospital systems around the country, which have already been targeted, are at risk for more attacks and that the U.S. government is doing too little to prevent breaches.

AT&T customers can visit att.com/DataIncident for more information.

Shares of AT&T Inc., based in Dallas, fell slightly on Friday.