1. A method performed by a computer system comprising a processor and a memory encoded with program instructions that, when executed by the processor, cause the system to perform the method, the method comprising: rendering a first identifier to a user of the computer system; receiving an input from the user, wherein the input represents a series of locations on the first identifier; determining, based on the input and the first identifier, whether the user demonstrates knowledge of a secret identifier; and authenticating or not authenticating the user based upon the outcome of said determining step.