An artificial intelligence, created by humans, is hostile to human beings.
HAL 9000, the computer tasked with running the ship Discovery, is tasked with simultaneously always providing helpful information, while also keeping the true nature of the mission secret. To resolve this contradiction, he decides to kill the crew members.
The Master Control Program is a program that manages the mainframe of the company ENCOM, who tries to defend the computer against Users breaking in.
CLU and RINZLER are a pair of corrupted programs both meant to protect Users (humans) but work to destroy them.