zlacker

TOTP codes are phishable and repayable in real-time - both via web (visiting the wrong site which asks for a TOTP and relays it within a few seconds), and via social engineering over the phone (give us one of the codes to prove it's you and we can keep your account safe).

Adding number matching or similar helps ensure that the same user is initiating the session as is approving it - an issue when people discovered that Microsoft (among others) would do push messages to authenticate a login, and that users (if spammed late at night with constant requests), would often eventually hit allow to stop the notifications.