T-Mobile US and its unit Metro PCS informed customers on August 23 about a potential security breach that was discovered and shut down by the company.
The cyber-security team found and shut down unauthorized access to certain information on August 20, and reported the matter to authorities, T-Mobile said in a statement on its website.
No financial data, social security numbers or passwords were compromised, but other personal information like name, email-id, phone number, zip code, account number or type (postpaid or prepaid) may have been exposed, the company said.
About 3 per cent of T-mobile's 77 million customers could have been affected, a company spokesperson told technology news website Motherboard.
T-Mobile did not respond to Reuters request for comment outside regular business hours.
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