I've got something for you to add to the topic post. Source: http://www.pcgamer.com/2010/06/07/brink-screenshots
Wedgwood took various primary objectives – to blow open a door, to hack a safe, to deliver information – and each was distinct and challenging. The hacking, for example, happened automatically after a device was stuck to a computer, but the process could be sped up if the player lowered his weapon and opened up his PDA. This leaves you vulnerable to attack, but if others come and join with their own PDAs or to provide covering fire, you can progress much faster.
Hacking occurs automatically while the hacking transmitter is attached to the objective, but progresses faster if the player makes an active effort to hack. So, you can attach the transmitter, stay by the objective to keep the signal strong, but keep alert and ready to fight instead of speeding the hacking process, OR you can place the transmitter, go and hide so you can devote your attention to actively hacking, but suffer from a weakened signal that slows your progress.