The first, two-step verification, has been offered for several years. It prompts you to enter a four-digit code when you sign into your iCloud account, purchase something from one of Apple’s stores on a new device, or make changes to your Apple ID. Those codes were delivered by push notification to an authenticated device of your choosing, or via SMS text message. It also necessitated the use of “app-specific passwords” (long random passwords generated by Apple) to log into accounts and services that didn’t support the two-step verification process, and provided a Recovery Key to store as an override, should you be unable to receive the relevant code any other way.
The newer two-factor authentication is an improvement upon that process, which Apple started rolling out last year. While the principle is similar, the execution is refined. The verification code is now six digits and is automatically sent to all of your authorized devices. When a new device is logged into your iCloud account, you’re also shown the rough location of that device (on a city level), so that you can be sure it’s not someone halfway around the world trying to gain access; there are also buttons to allow or deny that login. Authentication only happens when you log into your iCloud account from a new device for the first time, or when logging into an account on the web. (In the latter case, you can choose to trust your browser so you don’t have to do that every time.)
hope this helps.
10-28-2016 10:55 PM