From Craig S Wright, vice president of Global Institute for Cybersecurity + Research, a look at the use of SCADA systems that are connected to the Internet. You probably remember SCADA from the starring role it played in the Stuxnet worm.
For those who do not know, 747's are big flying Unix hosts. At the time, the engine management system on this particular airline was Solaris based. The patching was well behind and they used telnet as SSH broke the menus and the budget did not extend to fixing this. The engineers could actually access the engine management system of a 747 in route. If issues are noted, they can re-tune the engine in air.
The issue here is that all that separated the engine control systems and the open network was NAT based filters. There were (and as far as I know this is true today), no extrusion controls. They filter incoming traffic, but all outgoing traffic is allowed. For those who engage in Pen Testing and know what a shoveled shell is... I need not say more.