The current invention is a blocking device that provides read and write protection for computer long-term storage devices, such as hard drives. The blocking device is placed between a host computer and the storage device. The blocking device intercepts communications between the host and the storage device and examines commands from the host to the storage device. Certain commands, such as commands that may modify the storage device, may be discarded. The current invention enables multiple host computers to communicate to the blocking device. The current invention selectively blocks only specified host computers.