Abstract: A method for authenticating a user includes receiving a request for access from a user claiming to be a particular user. A first challenge having a first level of complexity is transmitted to the user. A response to the transmitted first challenge is transmitted. A determination is made as to whether or not the transmitted response authenticates the user as the particular user. The requested access by the user is allowed if the transmitted response authenticates the user. However, a second challenge having a second level of complexity, greater than the first level of complexity, is transmitted to the user if the transmitted response does not authenticate the user.