1
general::
Disseminate or circulate very quickly, as in The rumor about their divorce spread like wildfire. The noun wildfire means "a raging, rapidly spreading conflagration." [c. 1800]
American Heritage Idioms
2
general::
Phrase(s): spread like wildfire
Fig. [for something] to spread rapidly. • Rumors spread like wildfire when people are excited. • This disease will spread like wildfire when it gets going.
McGrawhill's American Idioms And Phrasal Verbs