[EvanAnderson]

Why destroy the computers? Just destroy the power grid. Get a few million smart meters to disconnect from the grid simultaneously and watch the sparks fly. Destroy a sizeable quantity of transformers and it will be months or years before power is restored.

I think this is more "movie plot", though. "Smart Grid" security has gotten tons better than it was at the start. A lot of very security conscious and smart people have been working on it.

[wegs]

Precisely what you said: Power grid has security. Compromising 90% of connected devices with a mainstream OS would, at once:

(1) Tank the economy

(2) Likely, be doable with resources totaling in the single-digit million dollars

Modern wars are largely about industrial capacity.

But if it is equally easy to compromise the grid, why not do both?

This may sound like a movie plot, but so did the invasion of Poland at the beginning of WWII, the attack on Pearl Harbor, nuclear bombs on Japan, the rape of Nanjing, or many other actual events which Actually Did Happen.

We tend to underestimate the impact of rare events: our brains are conditioned to discount anything which happens once or less than once per lifetime. That's likely why humanity will kill itself at some point.