Over two years, a hack of Experian apparently acquired the records of 15 million T-Mobile customers and people who had applied for credit. Experian, the vendor that processes T-Mobile's credit applications.
T-Mobile's CEO posted a letter on the company's website to explain:
We have been notified by Experian, a vendor that processes our credit applications, that they have experienced a data breach. The investigation is ongoing, but what we know right now is that the hacker acquired the records of approximately 15 million people, including new applicants requiring a credit check for service or device financing from September 1, 2013 through September 16, 2015. These records include information such as name, address and birthdate as well as encrypted fields with Social Security number and ID number (such as driver’s license or passport number), and additional information used in T-Mobile’s own credit assessment. Experian has determined that this encryption may have been compromised. We are working with Experian to take protective steps for all of these consumers as quickly as possible.