When you do the hack, you can go all the way around to the back of the wall it's on (during the solo one, at least) and just hide behind that to do the hack. That's how I did it, the rest of it really isn't that difficult. Just make sure you refill your ammo before you start to give yourself an edge, and I like to throw a grenade down before I start the plant, so that the bots coming at me just get knocked down to give myself more time. I hope any of that helps you, it was really frustrating for me before I found out I could go to the back of the wall to do the hack without getting shot.

Set a turret to the far left-hand back corner facing towards the enemy spawn and beneath the stairs. Draw the enemy in the line of fire, then run like a bat out of hell (I was a light) to fix the engineer station. Don't worry if you can't do it all, engineer is a progress meter. Do this step again with the turret setup and draw the enemy fire. Many times its better to wait for a medic to revive you. Once you fix the engineer portion, comes the real hard part, the operative. You must (this is for 3 star) try to get a disguise. Or parkour your ass ninja style to the hack box. Once you start hacking, don't run away, you will just get shot or it will take too long. Crouch down with the hack going, and back up about 3 spaces to your left there is a box there you can use for cover. Face their spawn, and edge back and forth to avoid their gunfire. Once you get the hack part complete, you will need at least a minute and just parkour your butt to the drop box and upload that data!