Described is a computer system which is coupled to a remote computer via a data communication link. The computer system has a normally closed enclosure and is capable of securing data retained within the system against unauthorized access. The computer system includes an erasable memory element mounted within the enclosure for selective activation to active and inactive states and for receiving and storing a security password when in the active state. A manually operable option switch is mounted within the enclosure. The option switch is operatively connected with the erasable memory element and manually settable by a user of the computer system for setting the erasable memory element to the active and inactive states. A communication line detector is operatively connected with the erasable memory element for detecting a disconnection of the data communication link and for clearing any stored security password from the erasable memory element in response to a change of the communication link detector between a first state and a second state.