"Customer proprietary network information (CPNI) as defined by the Federal Communications Commission (FCC) rules was accessed," the company said in a security update.
"The CPNI accessed may have included phone number, number of lines subscribed to on your account and, in some cases, call-related information collected as part of the normal operation of your wireless service", it added.
Earlier breaches at T-Mobile exposed customers' information in 2018, prepaid customers' information in 2019 and exposed customer and financial data in March last year, the report mentioned.
T-Mobile said the fresh breach affected a "small number of customers (less than 0.2 per cent)."
T-Mobile has approximately 100 million customers, which equates to around 200,000 people affected by this breach.
The company was alerting affected customers that a "security incident" exposed their account's information.
"The data accessed did NOT include any names associated with the account, financial data, credit card information, social security numbers, passwords, PINs or physical or email addresses," T-Mobile said.
(Only the headline and picture of this report may have been reworked by the Business Standard staff; the rest of the content is auto-generated from a syndicated feed.)
Business Standard has always strived hard to provide up-to-date information and commentary on developments that are of interest to you and have wider political and economic implications for the country and the world. Your encouragement and constant feedback on how to improve our offering have only made our resolve and commitment to these ideals stronger. Even during these difficult times arising out of Covid-19, we continue to remain committed to keeping you informed and updated with credible news, authoritative views and incisive commentary on topical issues of relevance.
We, however, have a request.
As we battle the economic impact of the pandemic, we need your support even more, so that we can continue to offer you more quality content. Our subscription model has seen an encouraging response from many of you, who have subscribed to our online content. More subscription to our online content can only help us achieve the goals of offering you even better and more relevant content. We believe in free, fair and credible journalism. Your support through more subscriptions can help us practise the journalism to which we are committed.
Support quality journalism and subscribe to Business Standard.