I have to disagree somewhat with your sky-is-falling viewpoint. A few policy changes followed by some precautions can protect entire systems similar to this. Step 1, create bulletproof policy and *enforce* it strictly. In NBC facilities, this is easy: you imprison people. In other cases, such as the "omg hackers in the power grid" power grids, you fire them and sue them in civil court because you *do* have a valid contract in your jurisdiction. As for protections, maintain an air gap in all cases. This is easier than most people think. First, unplug everything that isn't essential. Second, reduce cabling at the breaker panel and the switches so that it is impossible to plug something else in and have it work. Third, fill every unnecessary computer port with epoxy cement and epoxy cement all keyboards and mice into their own ports. Terminals are typically redundant in these establishments, so unless you fuck up all of your terminals in all of your redundant locations, you'll be fine. These few, minor tasks are easily surmountable in these large organizations.