Prevention of unauthorized scripts

Methods and system of preventing unauthorized scripting. The invention includes providing one or more tests to a user for distinguishing the user from a machine when the user requests access to the server. By storing information on a correct solution to the test in a block of data and sending the block of data together with the test, the invention provides stateless operation. Moreover, maintaining a database of previously used correct responses prevents replay attacks. The invention also includes providing combinations of alternative tests, such as visually altered textual character strings, audible character strings, and computational puzzles. Other aspects of the invention are directed to computer-readable media for use with the methods and system.