I remember a rule a controls engineer once told me: never connect the plant to the Internet. Nothing clever, no humorous quip, no deep insight. Just don't do it. If you do need to get data out to the living world, and you will, then you carefully set up individual firewall rules just for the data system - which very much can not drive the process system.

This is where I begin ranting on the topic.

Why? Because plants aren't secure. They're meant to run all the time by people who may or may not know how to properly use a mouse. There will be passwords taped to monitors, systems that automatically log in to prevent start up delays, and authentication of the order that it-better-just-work-by-default. Under no circumstances should that damn system ever, ever be exposed to the outside world. Not by Ethernet, wireless, or flash drive. It's a young innocent facing the cruel, brutal internet; it's going to get hurt.

New plants are fancy and have highly trained workers with brilliant industrial IP wireless systems with state of the art VM servers and oh god did that guy just plug his phone charger into the damn wrapper HMI and now Windows media player has popped up and no one can acknowledge alarms (this partly why PCs tend to be in large metal boxes, that and dirt/water). No imagine that sort of silliness, but driven by the less savory from outside the intranet.

Just don't risk it. You'll never have a problem, and no one is ever going to care enough to hurt the plant... Except but for that one time when suddenly all the convenience and hubris won't bring back the machine that just slagged itself from some malicious command from outside.