System for preventing unauthorized acquisition of information and method thereof

A server apparatus includes: an output detector for detecting output-processing which is processing of outputting data from the application program into a shared area; and an output control section for storing instruction information in the shared area, instead of storing the output data outputted from the application program therein, in response to the detection of the output-processing, the instruction information specifying an acquisition method by which an authorized client apparatus acquires the output data. The client apparatus includes: a reading detection section for detecting reading-processing which is processing of reading data from the shared area; and a reading control section which reads the instruction information from the shared area in response to the detection of the reading-processing, and which acquires the output data by the acquisition method specified by the instruction information.