Abstract: A computer security decide for discouraging or preventing unauthorized entry into computer systems and for preventing the unauthorized copying of proprietary computer software or data in a computer system is disclosed. The security device is based at least in part in hardware and comprises logic device means, such as a programmable logic array or a ROM, for recognizing a group of signals present on a bus indicative of unauthorized copying efforts, latch means for remembering the detection of unauthorized copying efforts, and switching device means for interrupting the flow of DC supply power to preselected components or memory locations within the computer system containing memory whose contents is to be protected to render said components or locations inaccessible.