In episode terrain, play level 04, "The Jacobs Installation." You should start out in a room with one door. Bring Raynor and only Raynor through the door and through the hall (don't open any doors yet). There should be a missle wall trap at the end of the hallway, don't destroy it, instead go through the hallway at the top right of your screen. Down the hallway there should be an orange civillian. He will ask for mercy and says he will give you a cheat if you spare him. Go on past him without killing him, use the portal and activate the security cameras and go back past him. Now, bring the rest of your force and continue with the level by going through one of the top doors and he will tell you he is grateful for you not killing him and he gives you the cheat.