Basically to get this you have to go through every ending in the game. You don't necessarily have to finish each walkthrough though. As long as you get to Act 4 you can quit and start up the next one. Just make sure you finish the ending at least once!
Some good tips for this one is:
1. Look for good places to blow a path through. A good placed explosion can save you a good minute sometimes.
2. Once you get the almighty virus every single one of these are easy. Simply send one virus and about 5 attackers. In other words hit Y once and A 5 times. Then rinse and repeat until you're out of energy. Then let it recharge and start again.
Although on about half of the hacks you won't even need to send in the second wave after the recharge.
And that's that. Simply follow those 2 rules and any System Override Hack is easy. Happy Hunting! :D