Invalidity monitoring program, invalidity monitoring method, and invalidity monitoring system

For use in monitoring invalid data that causes a computer to execute an invalid operation there is provided, an invalidity monitoring program that can monitor input/output data sent to and received from not only a network but also an externally connected device and that allows a user to set a variety of invalidity determination rules and apply an efficient rule. A data acquisition unit (14) acquires input/output data, flowing on a network or an externally connected bus, and the ID of an operator. An invalid operation determination unit (15) determines whether an operation is invalid by acquiring attribute information on a user, corresponding to the ID, from a user data storage unit (12), by referencing a rule, corresponding to the attribute information, from the rules stored in an invalidity rule storage unit (13) and defined for the respective user attributes and, in addition, by referencing a rule that generally determines an operation as invalid regardless of the attributes stored in the invalidity rule storage unit (13). If it is found that the operation is invalid, an interruption processing execution unit (16) stops the processing to be executed by the operation.