If the makers of the simulation don't want information going in and out and they want it hack proof, they'll simply have it detect when someone has hacked it (because, by definition, it knows what everyone is doing and what they're experiencing). It will stop the simulation, fix how it got hacked, and then resume the simulation. The "hack" would always fail.,(reply>), Except to detect that they've been hacked, they would have to already be aware of that particular vulnerability in their system, and if they were aware of it, they wouldn't have gotten hacked in the first place. So a mathematical proof is really the only way to guarantee that no information can transit between the simulation and their "world".