KRTV, Great Falls, said the hacker used the Emergency Alert System to warn viewers of KRTV and the local CW affiliate of "dead bodies rising."
"Do not attempt to approach or apprehend these bodies as they are extremely dangerous," the scrolling warning read.
The station said the hacking came from an outside source and engineers are working to determine how someone was able to get control of the alert system.
The Great Falls Police Department told the Great Falls Tribune it received calls from concerned citizens who saw the warning. However, the department said officers have not been called by KRTV to investigate the hacking.