T-Mobile CEO apologizes for the hack that exposed data of 53 million people as the company faces class-action lawsuits over the breach

• T-Mobile CEO Mike Sievert apologized for a hack that exposed the data of 53 million people.
• "Knowing that we failed to prevent this exposure is one of the hardest parts of this event," Sievert said.
• T-Mobile also announced a partnership with Mandiant and KPMG to help the company with its approach to cybersecurity.

T-Mobile CEO Mike Sievert apologized Friday for a data breach that affected over 53 million people.

The company is almost done with its investigation, and the breach is contained, Sievert said.

"Knowing that we failed to prevent this exposure is one of the hardest parts of this event," Sievert wrote. "On behalf of everyone at Team Magenta, I want to say we are truly sorry."

"Bad actors" work endlessly to exploit and attack systems like T-Mobile's, Sievert said, adding that while the company tries to stay ahead of them, it did not live up to customers' expectations.

"We're fully committed to take our security efforts to the next level as we work to rebuild trust," Sievert added.

As part of the company's next steps, Sievert announced a partnership among T-Mobile, Mandiant, and KPMG LLP. Mandiant, a global security firm that has been working with T-Mobile since its investigation into the breach started, and KPMG, a consulting firm, plan to help T-Mobile with its approach to cybersecurity.

"This is all about assembling the firepower we need to improve our ability to fight back against criminals and building a future-forward strategy to protect T-Mobile and our customers," Sievert wrote.

T-Mobile said nearly all the 53 million customers had been notified of the breach. The information stolen from the customers includes names, addresses, dates of births, phone numbers, Social Security numbers, and driver's license information.

T-Mobile became aware of the data breach after hackers posted in an underground forum, Vice's Motherboard first reported.

Since then, customers have filed class-action lawsuits against the wireless carrier, alleging violations of the California Consumer Privacy Act, which allows any Californian the right to see all the information a company has saved on them and a full list of all the third parties that data is shared with, and the Washington State Consumer Protection Act.