urban myth 
(also North American urban legend)
noun
A humorous or horrific story or piece of information circulated as though true, especially one purporting to involve someone vaguely related or known to the teller.Starting with a friend's e-mail claiming a renowned urban legend as a true story about a mate, Manford reveals the truth about countless childhood horror stories....
- A more obvious type of myth is that of urban legends, improbable stories of events happening to unknown people on an unspecified date.
- We are not talking about armour here, we are talking about email chains that get circulated, some of which become urban myths and some becomes information and news to others.