Use the following trick to hack into a computer without getting detected. Start by rappelling down the building as usual, until you see a guard. Then, take a clear shot at his head. Once this is done, break into the window, grab his grenade, and shoot out all the lights in the room. Then, check the computer. When the guards come running in, fall out the window that you came in through. Hang until they all are gone. When the shocking music stops, get up and check the computer again. Finally, go out the door and turn left. Go through the door that was previously jammed. Run to the bottom and grab the medikit; then go through the door. Quickly turn around to face the door. Throw the grenade to kill the guard pursuing you. Make sure you are far enough away to avoid injury. Hop on the pipe and slide down to the bottom. If you are quick enough, you can see how the guard was killed by your partner.