A preliminary analysis also signaled that information on just over 40 million additional people who applied for credit from T-Mobile was also stolen.

No phone numbers, account numbers, PINs, passwords, or financial information was compromised for most people, according to the company. However, the phone numbers, account PINS, and names of about 850,000 prepaid customers were exposed.

The discovery came after a hacker claimed in an online forum this month that they had stolen data from T-Mobile.

The company became aware of the claim and launched an investigation.

Cybersecurity experts tapped by T-Mobile identified an access point believed to be used by the hacker and closed it.

This week, experts verified that some data was accessed by hackers, and began coordinating with law enforcement.

"While our investigation is still underway and we continue to learn additional details, we have now been able to confirm that the data stolen from our systems did include some personal information," the company said.

The stolen data includes customer names, dates of birth, social security numbers, and driver's license information.