I'd gotten the idea from reading an article awhile back about this sort of issue. It can effect power plants, water treatment facilities, traffic signaling devices, etc. Including the story of the sign pictured here, as well as similar stories. (Simply run a Google search for "zombie attack highway sign" for more stories.)
This morning, I see the following in my email from ZD Net:
U.S. Emergency Alert System open to more 'zombie' hackers after accidental SSH key disclosure
No, it's not funny. Not really. Well, yes, it's frakking hysterical, but only on the surface.
The problem is, if someone wanted to do something nefarious by gaining entrance to these devices. Or post something a little more plausible on the EAS system, maybe along the lines of the hacked AP tweet falsely reporting an attack at the White House.
Which then promptly tanked the stock market even though the hack was discovered immediately and the account disabled.
So while, yes, my story is fiction, it's scarily bolstered by facts. The fact is that foreign agents don't need to bomb us to drive our country into the ground. All they need are a few moderately talented hackers who can take down the systems we've come to depend on.
Something to think about, isn't it?