T-Mobile US said Friday that an ongoing investigation into a data breach has revealed that hackers have accessed the personal information of an additional 5.3 million customers, bringing the total number of people affected to more than 53 million.
The third largest US wireless operator announced earlier this week that the personal data of more than 40 million former and potential customers, along with data from 7.8 million existing wireless customers, had been stolen from T-Mobile.
In its latest update, released days after the US Federal Communications Commission (FCC) opened an investigation into the violation, T-Mobile identified 5.3 million additional cellular users affected by the violation and 667,000 other accounts of former customers.
The data includes addresses, birth dates and phone numbers of customers, the company said, adding it had no indication that the data retrieved contained financial information such as credit card or other payment details.
Some T-Mobile customers sued the company for damages in federal court in Seattle late Thursday night, saying in a proposed class action lawsuit that the cyberattack violated their privacy and put them at greater risk of fraud and identity theft.
The wireless operator is the latest victim of cyberattacks against large companies in the United States as hackers exploit the compromised privacy and security of user systems due to work from home policies in place since the beginning of the coronavirus pandemic.
In 2018, the company announced a potential security breach that could affect around 3 percent of its 77 million customers.
“T-Mobile has had 6 other data breaches in the past 4 years,” said Doug Schmidt, a professor of computer science at Vanderbilt University.
“It seems that their IT system is particularly vulnerable as they have not been able to fix their known security issues during this period, which should affect customers.”
T-Mobile said in an official application on Friday that it was confident of having “blocked access” during the ongoing investigation.