What is viral marketing? It encourages individuals to pass on a marketing message to others. It facilitates people to pass along a message voluntarily!
Off the Internet, there have been expressions as "word-of-mouth," "creating a buzz," "leveraging the media," "network marketing." But on the Internet it's called "viral marketing."
A few days ago I received an email from 'Bad Language' about illusionist Derren Brown’s televised 'Russian Roulette'. I became interested and went to Derren Brown’s site. Then I started searching in Youtube for his clips, and found a lot of his stunts and tricks on NLP, Subliminal Advertising etc.
So, that's how the viral marketing worked in this case: email --> Derren Brown's site on Russian roulette --> youtube --> other Derren Brown's clips.