Abstract: A data security device for a computer system controls the addition and removal of data using an external data drive. The computer system includes a microprocessor, memory, internal data storage, a power supply, and an external data drive. An access controller is coupled between the power supply and the external data drive. The access controller selectively makes or breaks an electrical connection between the power supply and the external data drive to prevent the addition or removal of data from the computer system using the external data drive. The access controller preferably includes a switch coupled to the power supply which has on and off states. A timer, coupled to the switch, generates a timing signal when the switch is in the off state for a first period. A switching device such as a relay or a transistor makes an electrical connection between the switch and the external data drive before the timing signal is received.