Participants in Singapore take part in a fake zombie apocalypse. ROSLAN RAHMAN/AFP/Getty Images

The zombie drama "The Walking Dead" normally airs on the American cable-television channel AMC on Sunday evening.

But on Monday, residents of two small American cities got treated to a zombie apocalypse over the air, courtesy of pranksters who apparently hacked into the Emergency Alert System at three broadcast stations.

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"Civil authorities in your area have reported that the bodies of the dead are rising from their graves and attacking the living," said an ominous voiceover that interrupted programming yesterday afternoon on KRTV-TV, a CBS affiliate in Great Falls, Mont., and on a KRTV subchannel that carries a CW network feed.

"Do not attempt to approach or apprehend these bodies as they are considered extremely dangerous," the voice also said as listings of affected counties scrolled across the top of the screen.

Around the same time, WNMU-TV, the PBS affiliate in Marquette, Mich., on the state's Upper Peninsula, was similarly pranked, according to local reports.

Later that evening, WBUP-TV, the ABC affiliate in Marquette, was hit by a "zombie alert" that scrolled across the bottom of the screen during the broadcast of "The Bachelor," according to the station's website.

According to the website of Radio magazine, there were reports that "zombie" hacks of the Emergency Alert System were attempted yesterday at TV stations in Salt Lake City.

The Emergency Alert System (EAS) is a national warning system run jointly by the Federal Communications Commission, the Federal Emergency Management Agency and the National Weather Service.

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Almost all broadcast, satellite and cable radio and television outlets are required to subscribe to the EAS, and EAS alerts can cut into programming at any time.

It's not clear how the EAS signal was hijacked in Great Falls and Marquette, but it's worth noting that both towns have large populations of college students.

KRTV in Great Falls said its engineers were trying to figure out what happened. Authorities in Great Falls took the news of walking dead in stride.

"We had four calls checking to see if it was true. And then I thought, 'Wait. What if?'" Great Falls Police Department Lt. Shane Sorensen told the Great Falls Tribune. "We can report in the city, there have been no sightings of dead bodies rising from the ground."

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