1. A method comprising: determining that a current user, that (i) fails to perform an authentication process for accessing a service or (ii) requests to perform a reset process for a user-authentication factor of said service, is a genuine user that is authorized to reset said user-authentication factor of said service, by performing: (a) presenting to the current user a fresh task that the current user is required to perform and that can be tracked by the service; (b) monitoring a manner in which the current user performs the fresh task; (c) extracting from said manner in which the current user performs the fresh, a fresh user-specific characteristic; (d) comparing between (I) the fresh user-specific characteristic, that is extracted from the manner in which the current user performs the fresh task, and (II) a previously-extracted user-specific characteristic that was previously extracted from prior user interactions of the genuine user; (e) if there is a match between (I) the fresh user-specific characteristic, that is extracted from the manner in which the current user performs the fresh task, and (II) the previously-extracted user-specific characteristic that was previously extracted from prior user interactions of the genuine user, then determining that the current user is the genuine user that is authorized to reset said user-authentication factor of said service.