Out-of-Band Authentication is one popular OOBA method is through text message (SMS). When a user tries to login from a new device or location, the service will send a single-use verification code to the user's registered phone number via text. The user then enters this code during authentication in addition to their password. This adds an extra layer of security by requiring the hacke... https://www.zupyak.com/p/4417355/t/out-of-band-authentication-a-growing-necessity-in-todays-interconnected-world