A program that is activated by the operating system after a predetermined period of inactivity by the user. A screensaver serves two goals: By blanking the screen or displaying a ­constantly-changing pattern, the screensaver avoids the burn-in effect on the screen’s photo-sensitive layers, through which a pattern displayed for longer periods of time remains visible as a ghost image on the screen. The second goal is to lock the access to the computer system after a period of inactivity. Users who return to their workstations have to enter their password to regain access to the computer.