An improvement to a graphics controller to prevent the contents of selected portions of the frame buffer from being read by devices external to the graphics controller. The invention defines one or more viewable rectangles in the frame buffer as a protected write-only area. Any attempt to read data from the protected area of the frame buffer triggers a security violation which can delete or destroy the contents of that area to prevent it from being read. The controller can also operate in a bypass mode in which the security functions are bypassed so the graphics controller operates in a conventional manner. A security violation may return the controller to the bypass mode. The invention can prevent protected data, such as copyrighted data downloaded over the Internet, from being copied from the frame buffer and used in an unauthorized manner.