A system and method for automatically determining if a computer user is a human or an automated script. Human interactive proofs (HIPs) are currently used to deter automated registration for web services by automated computer scripts. Unfortunately, HIPs entail multiple steps (request service, receive challenge, respond to challenge) that can be burdensome. The system and method of the invention in one embodiment provides a "black-box" to potential users consisting of a challenge generator and a secret key. The challenge is generated for the user and the response can be provided as part of the service request, eliminating the need for a separate challenge from a service provider and response to the challenge.