Earlier this year, T-Mobile suffered a massive data breach that saw data from over 50 million customers and former customers stolen. Now, a new report says T-Mobile has suffered another data breach, though this time on a significantly smaller scale.

According to a report from The T-Mo Report, internal documents show that T-Mobile suffered from “unauthorized activity” on some customer accounts. “That activity was either the viewing of customer proprietary network information (CPNI), an active SIM swap by a malicious actor, or both,” the report explains.

The report, which cites a handful of internal documents, shows that there are three main categories of customer affected by this breach.

Affected customers fall into one of three categories. First, a customer may have only been affected by a leak of their CPNI. This information may include the billing account name, phone numbers, number of lines on the account, account numbers, and rate plan info. That’s not great, but it’s much less of an impact than the breach back in August had, which leaked customer social security numbers.

The second category an affected customer might fall into is having their SIM swapped. This is where a malicious actor will change the physical SIM card associated with a phone number in order to obtain control of said number. This can, and often does, lead to the victim’s other online accounts being accessed via two-factor authentication codes sent to their phone number. The document says that customers affected by a SIM swap have now had that action reversed.

The third category is customers could have had both their private CPNI viewed as well as their SIM card swapped.

T-Mobile hasn’t publicly addressed this potential data breach. It’s also unclear just how widespread this data breach is, but it certainly seems to be far smaller than the previous data breach that the company disclosed in August. The August breach was far wider in scale and involved both social security numbers and driver’s license details.

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Chance Miller

Chance is an editor for the entire 9to5 network and covers the latest Apple news for 9to5Mac.

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