In a major data breach of credit reporting agency Experian, hackers have reportedly stolen personal information of 15 million people who applied to sign up for T-Mobile's service last month.
Those possibly affected include anyone who applied for a regular T-Mobile USA postpaid plan between Sept. 1, 2013 and Sept. 16, 2015.
That's because T-Mobile used Experian, a major credit bureau, to conduct credit checks on its customers.
T-Mobile CEO John Legere expressed his frustration in a statement Thursday.
"Obviously I am incredibly angry about this data breach and we will institute a thorough review of our relationship with Experian," Legere said. "I take our customer and prospective customer privacy VERY seriously."
According to Legere, hackers broke into the computer system in September, gaining access to a server full of sensitive information including names, addresses, Social Security numbers and birthdays.
CNNMoney reports that hackers could have attained other sensitive identification numbers, as well, such as ones issued on driver's licenses, military IDs or passports.
After the news broke, Experian stressed that the hackers didn't access multiple computer servers, and that T-mobile's breach was an “isolated incident.
Experian is now offering to provide T-Mobile applicants two years of free credit monitoring and identity protection.
CNNMoney cautions, however, that taking part “would require you to fork over more information to the company and confirm its accuracy.”