T-Mobile informed some customers recently that "bad actors" accessed their information, including social security and government ID numbers.
The company informed its customers that financial account information and call records were not part of the breach.
The company said that it has a number of "safeguards in place" to prevent a breach like this from happening.
T-Mobile said the safeguards "worked as designed" to alert the company of someone accessing customer information in February and March 2023.
Although financial records were not included in the breach, T-Mobile said some sensitive personal information might have been accessed.
"The information obtained for each customer varied, but may have included full name, contact information, account number and associated phone numbers, T-Mobile account PIN, social security number, government ID, date of birth, balance due, internal codes that T-Mobile uses to service customer accounts (for example, rate plan and feature codes), and the number of lines," T-Mobile told customers.
This was the second major breach T-Mobile has announced this year.
In January, the company said that 37 million customers were impacted. But in that breach, no social security or government ID numbers were taken, T-Mobile said.
T-Mobile said it reset pin numbers for affected customers. The company is also providing two years of credit monitoring to customers affected by the breach.
In a letter to customers, T-Mobile also encouraged customers to sign up for credit alerts from companies like Experian, Equifax or TransUnion.
Last month, T-Mobile revealed in an investor call that it has 114.9 million customers.
A request for additional comment has been sent by Scripps News to T-Mobile.
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