Hackers have stolen the personal information of about 15 million T-Mobile customers and potential customers in the U.S., including Social Security numbers, dates of birth and home addresses.
Experian says it notified law enforcement as soon as it discovered the breach, NPR's Laura Sydell reports:
She also says:
"T-Mobile uses Experian to check out the credit ratings of potential customers. According to Experian, the break-in affects anyone who applied for T-Mobile USA postpaid or device financing September 1, 2013, through September 16, 2015."
In a blog post on the company's website, T-Mobile CEO John Legere wrote that he was "incredibly angry" about the breach. He pledged that he "takes customer and prospective customer privacy very seriously."
Legere assured customers that T-Mobile systems had not been compromised and offered free credit monitoring for two years to anyone who may have been affected.
Experian said on its website that it doesn't know who was behind the hack and that it is taking "necessary steps" to prevent further breaches.
It directed customers to "remain vigilant" against identity theft and watch for phishing email scams that could ask for personal information like bank account numbers.
The Associated Press reports that nearly 800 data breaches were reported last year by U.S. organizations, according to the Identity Theft Resource Center.