Abstract: In order to enable an authorized user of a secured system to detect unauthorized use of that system, the system records identifying information about the user (e.g., a sample of the user's voice) each time the user uses the system. The system also plays back to the user the information recorded the last time that user used the system. If the user does not recognize the information played back or detects anything else wrong with that information, the user knows that someone else has gained access or at least attempted to gain access to the system by posing as him or her.