The US government system used to broadcast to the nation in times of national crisis can be hacked, researchers have warned.
The Emergency Alerting System (EAS) is set up to allow the US president to talk to the entire country within ten minutes of a disaster. It was introduced in 1997 after replacing an older system.
However, in research, security specialists IOActive said one TV network's output "was interrupted by news of a zombie apocalypse".
Lead researcher Mike Davis said the system needed to be re-engineered. IOActive has released guidance for concerned broadcasters wanting to protect their system.
Davis said, "In February we were shown an example of an intrusion on the EAS when the Montana Television Network's regular programming was interrupted by news of a zombie apocalypse."
He said, "Although there was no zombie apocalypse, it did highlight just how vulnerable the system is."
The message, which was also played on a radio station in Michigan, said, "Civil authorities in your area have reported that the bodies of the dead are rising from their graves and attacking the living.
"Follow the messages onscreen that will be updated as information becomes available. Do not attempt to approach or apprehend these bodies as they are considered extremely dangerous."
The broadcasters later had to apologise for any alarm or distress caused to listeners.
In the UK no such emergency broadcast system is in place, though the BBC says the government is set to launch trials later in the year for a new "public emergency alert system", that includes using the Internet, mobile networks and social networks.
A gov.uk document says, "The popularity of social media makes it an ideal platform for communication with people and for disseminating additional information in the aftermath of an emergency."