Hackers have stolen personal information belonging to about 15 million T-Mobile wireless customers, including Social Security numbers, home addresses, birth dates and other personal information.
The hackers got the information from credit reporting agency Experian, which T-Mobile uses to check the credit of its customers.
Experian said T-Mobile customers who applied for wireless service between Sept. 1, 2013 and Sept. 16, 2015 may have had their information stolen. T-Mobile told CBS News those affected may include people who applied but were turned down, as well as T-Mobile users.
Experian said it immediately notified law enforcement authorities after discovering the hack and that "there is no evidence to-date that the data has been used inappropriately."
The companies said that payment card and banking information was not affected.
T-Mobile customers can sign up for two free years of credit monitoring services at www.protectmyID.com/securityincident, a service owned by Experian. The company said that affected customers should "remain vigilant" against identity theft and watch for phishing email scams that ask for sensitive information such as bank account and Social Security numbers.
There have been a string of high-profile hacks of businesses and other organizations in recent years affecting millions of people, including adultery website Ashley Madison, Sony Pictures, the insurer Anthem, retailers such as Home Depot and Target, eBay and the U.S. Office of Personnel Management.
Nearly 800 data breaches were reported last year by U.S. organizations, according to the Identity Theft Resource Center.
"I am incredibly angry about this data breach and we will institute a thorough review of our relationship with Experian," said T-Mobile US Inc. CEO John Legere in a statement.
The Associated Press contributed to this report.