You need patience and timing to successfully hack the ctOS Control Center and escape without being drawn into a fight.
Objective: Locate a guard with the access code
Objective: Download access code
Get over to the northeast side of the ctOS Control Center and open the gate using the hacking point. Go through the gate and take cover. The guard on the left is the one with the code so wait for him to get close.
Objective: Hack the ctOS server
Objective: Leave the area
Now get moving to the south side sticking close to the building to make your way around. If you accidently leave the mission area you'll have to start again. Use the lift on the left of the south side gate to reach the roof, then access the cameras on the guards to the location and view of each guard.
When it's clear drop to the lower level and get to cover. When clear again move to the waypoint. The guards hang around for a while here but they do eventually move on so be patient. If you stick to the wall you can take down the one guard who hangs around and he won't see you coming.
Access the hacking point to start the minigame. Turn the middle point once then unlock the left point and turn it once. Unlock the bottom point and turn it three times and turn the timed point once.
Now unlock the far right point and turn it once. Unlock the upper left point and also turn it once.Turn the far right point twice to unlock the point at the top and access the camera. Using the camera on the far side of the room access the unlock point straight ahead.
To leave the area attract the guard nearby and and take him down. Head left and keep out of the way of the other guards between the you and the exit. Again, clear the white circle and you're free.