I built control computers for nuclear reactors. Those machines are not connected to a network and are guarded by multiple stages of men with automatic machine guns. It was designed to flawlessly run 3x triple modular redundant processed instruction-synced. They cycle and test each board every month.

What’s your source?

Almost all computers are insecure, not just the systems in nuclear stations.

Most operating systems are based on ambient authority, which is just a disaster waiting to happen.