Critical Infrastructure is not connected to the internet. They screamed this for 4 straight years on mad cow's show and the only time something similar has happened was Stuxnet and that's because

The reason for the discovery at this time is attributed to the virus accidentally spreading beyond its intended target (the Natanz plant) due to a programming error introduced in an update; this led to the worm spreading to an engineer's computer that had been connected to the centrifuges, and spreading further when the engineer returned home and connected his computer to the internet.

And that's just the narrative we were fed.