My friend is thinking of creating a game in which you hack into a fake safe/vault "A" and once you are in that "safe" you write code/create a firewall to stop the next person getting into that safe behind you (i.e. into safe "A") and then you work on getting into the next safe "B". He asked my advice on how difficult it would be for someone with a good coding knowledge to "hack" into the software of a safe (in game terms) and create a firewall behind them. I know it would proably depend on the level of protection of the software and the firewall and the programmers level but it would be great to know roughly how fesible this game would be i.e. if it would be really easy or only a hand full of people would be able to play it.
I did computer science over 10 years ago and have forgotten most of it (evidently) so I'm not much help to him so any thoughts would be very helpful.