this achievement is called Deadly Exploit its for reprograming the turrets in chapter 2 so they attack the rebels not you.
during chapter 2 you will come to a court yard filled with rebel solders and turrets you must snack past them to the apartments on the opposite side and make you way to the top floor you will come to a room with a single rebel talking to someone on a monitor kill him and hit the switch in front of the windows to re-program the turrets unlocking your achievement.