A computer implemented method for authenticating a user, the method including receiving an authentication request from a first computer system, the authentication request including an indication of an identity of the user to be authenticated; receiving one or more authentication factors for verifying the identity of the user, the one or more authentication factors including at least one authentication factor obtained from a second computer system associated with the user having the indicated identity; receiving an auxiliary authentication factor, the auxiliary authentication factor comprising data for verifying that the second computer system is currently in the possession of the user having the indicated identity; and verifying the identity of the user based on the one or more authentication factors and the auxiliary authentication factor.