It's not terrorists, it's organized crime

Important to note, "outside the US," in this vague warning/report.

Hackers literally turned out the lights in multiple cities after breaking into electrical utilities and demanding extortion payments before disrupting the power, a senior CIA analyst told utility engineers at a trade conference.

You figure this is likely targeting smaller countries without the resources to stop or catch them, but as an "it can be done" test case, it's interesting.