Like wildfire

A wild fire is of course, a destructive conflagration that gets out of control, but this is not thought to be the origin of the expression that something ‘spreads like wildfire’. It is believed the expression derives from ‘wildfire’ as an alternative name for Greek fire, which was a combustible, incendiary weapon used in ancient warfare, and so-called because it was invented by the Greeks in the Eastern Roman or Byzantine Empire around 672 AD. The figurative usage of something ‘spreading like wildfire’ dates from the 1300s. See also Greek fire.