SMS verification

Confirming that a user controls a phone number by sending a one-time code by SMS and asking them to type it back.

SMS verification is the check where a service sends a short code to a phone number and the user proves control of that number by entering the code. Platforms use it to slow down bulk account creation, to add a second factor at login, and to attach accounts to something scarcer than an email address.

Its weakness as a security factor is well documented (SIM swaps, SS7 attacks), so security-critical systems prefer authenticator apps. Its strength as an anti-spam gate is exactly why nearly every large platform still requires it at sign-up.