A method of authentication is disclosed. When a user registers with an enterprise, the enterprise instructs the user to select sounds from a selection of sounds. Any sound that the user selects is designated as a “type-A” sound and any sound that is not so designated is deemed a “type-B” sound. To authenticate the user, the enterprise combines type-A sounds and type-B sounds into a temporal series of sounds and constructs questions about the series that can only be answered by someone who can recognize and distinguish type-A sounds from type-B sounds. The series of sounds and the questions are then transmitted to the user. If the user is able to answer the questions, then he or she is authenticated, and if not, then he or she is not authenticated.