T-Mobile has unveiled Account Takeover Protection, using PIN numbers to protect lines from being migrated out by bad actors.

SIM swapping has become a major problem. According to Mozilla, the practice gets its name from a bad actor calling a carrier and impersonating a subscriber in order to have the customer’s phone number assigned to a new SIM card.

The SIM swapping scam starts with a person impersonating you as they contact your mobile carrier. They will claim that they have a new SIM card to activate for your account. They might say the original phone and SIM card were lost, destroyed or sold with the SIM card left in accidentally.

T-Mobile is now joining AT&T and Verizon in supporting PIN number protection, requiring a predefined PIN number before a number can be swapped out.

While this may be a minor inconvenience for individuals legitimately looking to transfer carriers, it’s a much-needed security feature to protect users from bad actors.