An intermediary data handler is used in a Secured Data Storage Subsystem (SDSS), to provide a host electrical computer system with security of certain data stored in memory of the computer system's static data storage device. The intermediary data handler is functionally disposed between the operating system (OS) and data storage device of the host computer. The data handler has Processor, Memory, and User Interface circuits, and resident software adapted to generate mocked-up response data in reply to an unauthorized read/write communication from the OS, the mock data response being automatically formatted to have a content and data-structure format acceptable by the host OS, while isolating and controlling the original communication from the OS. The SDSS includes host software adapted to integrate operation and function of the intermediary data handler with the host computer system to accomplish the security of data stored on the storage device.