Wiktionary
scare story
n. (context idiomatic English) A rumour spread by a scaremonger in order to cause anxiety.
Usage examples of "scare story".
I'd heard nothing, and according to the scare story the town would be blotted out if they were right.
Blaise knew, everyone knew, that whenever Hearst was in need of a scare story for his newspapers, he would invoke the Yellow Peril.
It would be very unprofessional, of course, but Novak wasn't going to go to the press with a scare story.