Traditional embedded systems used micro controllers. Or for plants they used PLCs for automation. People have been warning for years that connecting factory automation (or power plant control) to the network gave it an interface to the whole world. IT insisted that it would be on a subnet or in some other way "safe". And besides, no hackers in the PC space knew anything about the hardware and software in these systems.

The world is converging to point where everything is just an SoC capable of running a full OS and applications. IoT is just marketing taking advantage of the capability.