In fiction, there is a common trope where the villain of the story takes over all the television stations. He then taunts the hero by threatening Gotham’s water supply, or telling the populace they can’t trust the government, or even telling the President that a terrorist attack is coming but he’ll never know when or where. Is this even possible? In our modern age, could someone hack a satellite or cable provider, and take over the airwaves?
It is theoretically possible but technically very difficult even for one station especially because most people get their TV from cable these days. Hijacking all stations and methods of transmission would be nearly impossible in a practical sense. However, it has been done on a limited scale in at least one major market. Someone hijacked two stations in Chicago on November 22, 1987 in what is known as the Max Headroom broadcast signal intrusion. The culprits and their motives have never been identified. There have been other targeted broadcast signal intrusions as well but they are generally limited to one station and not every station in an area.
Following is a listing the JUST the satellites which can broadcast to America. Note there are many many satellites! (Unlikely anyone could hack so many all at once.)
Plus those are downlinked to local cable TV “head ends”. People at each one of those (one for each U.S. city basically), could easily “pull the plug” on any or all stations.
The thing you see in movies that can’t be done in real life is simultaneously turning on all of the TVs to broadcast your message. There’s no protocol in the TV stream that would allow TVs to be turned on remotely and TVs are sufficiently diverse that you wouldn’t be able to find a security hole in all of them that would allow for this exploit.
it’s possible to control the power state of devices which support HDMI CEC but I don’t know if there is a way to put something in the cable or OTA stream to do anything with it (I’d guess not.)
What if someone was able to hijack the Emergency Alert System/Emergency Broadcast System? That’s designed to transmit to all TV stations and cable systems.