URBAN LEGEND: a modern day folktale that appears mysteriously and spreads spontaneously in various forms, containing elements of humor or horror (the horror often "punishes" someone who flouts society's morals or conventions).
Urban legends often have a basis in fact, but are intriguing because of their ever changing lives after the fact.
Considering the present state of the media, urban legends can be very valuable sources of information. -- They can also be full of shit. -- One thing's for certain; it should never cost you a damn thing.