Two-factor authentication via SMS (left) and an alternative trusted iOS device (right)
Setting up two-factor authentication through text messages is one of the most popular ways users add another layer of security onto an account, on top of a basic password, including those for Apple's own software, like Apple ID and iCloud. Other than SMS, Apple allows users to implement two-factor authentication through a simple push notification sent to another "trusted device," or a phone call.
If the out of band verification is to be made using a SMS message on a public mobile telephone network, the verifier SHALL verify that the pre-registered telephone number being used is actually associated with a mobile network and not with a VoIP (or other software-based) service. It then sends the SMS message to the pre-registered telephone number. Changing the pre-registered telephone number SHALL NOT be possible without two-factor authentication at the time of the change. OOB using SMS is deprecated, and will no longer be allowed in future releases of this guidance.The new guidelines also make a point for companies to ensure that two-factor