A hoaxer who hacked a local news station in America and broadcast footage of a zombie apocalypse also managed to hack the national emergency alert system, police said.
The hoax was first thought to have been broadcast only on a local CBS station in Montana, but it was also played on ten emergency stations in Montana, Michigan, California, Utah and New Mexico, Greg MacDonald, CEO of Montana Broadcasters Association, said.
The FBI is now investigating, insisting that the issue is more serious than it first appears.
The Emergency Alert System is a national warning network in the US designed to address the public at times of dire need.
It is currently thought the message did not originate in the US, but the identity of the hacker has not been confirmed.
The warning broadcast across the US stated:
"Civil authorities in your area have reported that the bodies of the dead are rising from the grave and attacking the living.. [do not] approach or apprehend these bodies as they are extremely dangerous."