***"You can imagine a conflict when one party of the conflict sets fire to every home in the country that's on the other side of the conflict."***

Mikko Hypponen of F-Secure

I don't think we will have to wait 20 years for this.  Hackers are already cutting power.  In extreme temperatures (hot and cold) this will kill people.  

Mikko Hypponen gave a talk at Black Hat 2017 recently. 
I had a look for it so I could resteem it.  
But it is not here yet or I can't find it. 
I am sure a video will be published soon.  

Here is a link to an article about the talk by Bradley Barth from the Cybersecurity Source about the talk.  

https://www.scmagazine.com/researcher-in-two-decades-adversaries-at-war-could-cause-mass-destruction-via-iot-attacks/article/678053/