1. A method of protecting value documents and restricted information controlled by a data processing system against unauthorized issuance from an output unit operated by the system, comprising providing a special storage area which cannot be modified by a system user for storing output instructions which may be executed by the system to actuate the output unit to issue a value document, providing another storage area into which an operator may load programs and data, detecting whether a current instruction provided for system execution is an output instruction, sensing if each output instruction detected by the detecting step originated in the special storage area, permitting the output unit to be actuated by the output instruction when the sensing step senses origination of the current instruction from the special storage area, and stopping the output unit from issuing any value document under control of the output instruction when the sensing step senses the output instruction did not originate in the special storage area.