It's catching!
Viral marketing is a powerful tool. Done well, it can promote an offer, build a database, and even propel a brand from obscurity to global fame.Great viral marketing enables you to create a communication that is experienced by a huge number of people. Human beings have a great propensity to share - jokes, special offers, games; they just can't help passing them on.
Viral marketing not only allows you to exploit this trait of human nature, it allows you to exploit other's resources in order to get your message across. Great viral literally does take on a life of its own.