T-Mobile has had another data breach, although a report suggests this one is less severe than the one in August. Only a small set of customers have been affected, but they could be vulnerable to a SIM swapping attack.
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.