Do the "Day 3: Smash and grab" campaign mission for this as operative class. You'll be on security automaticly, fight your way down to the controls that you must hack as operative. Keep watch on the hacking meter, once its 95% or above, like 97-98%, it doesn't matter, just don't hit 100%. Now you will need to take down an enemy, either a player or a bot, and take their disguise, which the operative can do as the only class. You can also claim a disguise from a fallen enemy too whom was killed by another player or a allied bot. Hurry back to the almost finished hacking device while disguised and finish the meter to 100%. A cutscene will play and the achievement will unlock immediately. Keep in mind that enemy players or bots can remove the hacking device within a few seconds, should you have been killed or move away from the area of the controls.