Researchers reveal what data T-Mobile allegedly leaked in a data sample of 64M records

Attackers recently claimed to have breached T-Mobile, America’s second-largest mobile carrier, posting a dataset on a popular data leak forum. The post alleges that 64 million customer records were stolen as recently as June 1, 2025.

The Cybernews research team analyzed the data sample attached to the post on the forum to verify the nature and sensitivity of the leaked information.

The analysis found that the dataset contains a trove of highly sensitive user details:

  • Full names
  • Dates of birth
  • Tax IDs
  • Full addresses
  • Phone numbers
  • Email addresses
  • Device IDs
  • Cookie IDs
  • IP addresses

If the data in the leak were new, researchers believe that individuals impacted face serious privacy concerns.

Leaked sample shows old and new data

T-Mobile has experienced multiple data breaches in recent years. The company previously agreed to pay over $15 million in fines for four separate incidents, two of which compromised the data of tens of millions of users.

Moreover, the Cybernews personal data leak checker indicates that at least some of the emails in the data sample were included in previous T-Mobile breaches.

However, certain fields — such as phone numbers — appear to be new, increasing concerns that this may represent a fresh breach. The full scale and authenticity of the 64 million records have yet to be confirmed with 100% accuracy.

To read the full research report, please click here.

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