US Patent 9639689 User authentication

There is disclosed a technique for use in authentication. The technique comprises selecting an authentication challenge when an authentication request is deemed risky. An attack threat determined to be associated with the authentication request acts as a decision factor in the selection of the authentication challenge such that a biometric challenge is selected in the event that the attack threat describes a stolen device and an out-of-band challenge is selected in the event that the attack threat describes a stolen identification credential.