The No. 3 mobile-service provider in the U.S. says an additional 5.3 million customers had their addresses, birthdates and phone numbers accessed by hackers. That's on top of the 7.8 million subscribers the company earlier this week had said were affected.
"Our investigation is ongoing ... but at this point, we are confident that we have closed off the access," the company said in a filing with the U.S. Securities and Exchange Commission.
Earlier this week T-Mobile said that in addition to the 7.8 million -- now 13.3 million total -- active customers whose data was compromised, more than 40 million records of former and prospective customers were also accessed in the hack.
On Friday, the company said it identified another 667,000 accounts of former customers whose names, dates of birth and phone numbers were compromised.
This past weekend, Motherboard first reported that it was in contact with the hackers, who claimed to have access to the data of millions of T-Mobile users.
T-Mobile has nearly 105 million customers and has been targeted by hacks multiple times in recent years.
In December, the company said that information regarding about 200,000 of its customers was illegally accessed. In 2019, the company said a "small number" of its prepaid customers were affected by a hack. And in 2018, a data breach affected more than 2 million customers.
At last check T-Mobile shares were trading off 0.7% at $139.96.