San Francisco: US telecommunications giant T-Mobile has confirmed that recent reports of a new data breach are linked to notifications sent to a "very small number of customers" who fell victim to SIM swap attacks, media report says. "We informed a very small number of customers that the SIM card assigned to a mobile number on their account may have been illegally reassigned or limited account information was viewed," a T-Mobile spokesperson was quoted as saying by BleepingComputer. "Unauthorised SIM swaps are unfortunately a common industry-wide occurrence, however this issue was quickly corrected by our team, using our in-place safeguards, and we proactively took additional protective measures on their behalf," the spokesperson added. According to the report, T-Mobile refused to provide additional details when asked for more info on the total number of affected customers and the method used by the attackers to pull off the SIM swap attacks successfully. Also ReadFortnite servers back online after major outage A recent report said that affected customers fall into one of three categories. First, a customer may have only been affected by a leak of their customer proprietary network information (CPNI). This information may include the billing account name, phone numbers, number of lines on the account, account numbers, and rate plan info. In 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 the 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 final category is simply both of the other two. Affected customers could have had both their private CPNI viewed as well as their SIM card swapped.