Abstract: A computer system for reading encrypted information is disclosed. A unit (24) for decrypting the information is open only as long as a display tool (A4) occupies a system-modal operative mode (SM). In this system-modal operative mode, the display tool (A4) emits, to the decrypting unit (24), a predetermined enabling signal (BS) without which the decrypting function does not work. When the display tool occupies the system-modal operative mode, the user does not have access to the user functions not defined by the display tool, thereby preventing unauthorized copying, storage and the like of the decrypted information.