About 15M T-Mobile users affected by Experian data breach

According to Experian, T-Mobile customer data logged between Sept. 1, 2013 through Sept. 16, 2015 was taken in the security breach. The attackers came away with names, dates of birth, addresses and forms of identification like Social Security numbers and drivers' license numbers, as well as other information required by T-Mobile's internal credit assessment system.

Experian said the breach did not expose payment or banking information, nor did it affect the firm's consumer credit database.

"We take privacy very seriously and we understand that this news is both stressful and frustrating. We sincerely apologize for the concern and stress that this event may cause," said Craig Boundy, CEO of Experian North America. "That is why we're taking steps to provide protection and support to those affected by this incident and will continue to coordinate with law enforcement during its investigation."

Affected users should receive notifications directly from Experian, which is offering those impacted two years of credit monitoring through ProtectMyID. Users can visit an FAQ webpage for more information.

T-Mobile CEO John Legere commented on the matter via Twitter and the carrier's official blog, but didn't offer much insight into the attack beyond what was already provided by Experian.

"Obviously I am incredibly angry about this data breach and we will institute a thorough review of our relationship with Experian, but right now my top concern and first focus is assisting any and all consumers affected," Legere said.

Today's data breach comes at a crucial time for America's third-largest cellular provider. Legere and company are trying to woo customers from market leaders Verizon and AT&T with aggressively priced payment plans, data incentives and contract-free services. With the recent launch of iPhone 6s, for example, T-Mobile sparked a minor price war after announcing a promotion that nets upgraders a new iPhone from $5 per month with trade-in, assumedly after a credit check.