The only thing that I can say about it, is that most (if not all) vital systems (power plants, traffic control, water supply,...) are not linked to the internet in any way. All power plants for example have two totally independent systems. The system responsible for the functioning of the plant never sees the outside (as the outside never sees that system). And I doubt they run 2k, too, actually... I'm pretty sure they use systems you and I have never even heard of... (Powerplant OS 2003...yay)