Viral marketing and viral advertising refer to marketing techniques that use pre-existing social networks to produce increases in brand awareness, through self-replicating viral processes, analogous to the spread of pathological and computer viruses. It can be word-of-mouth delivered or enhanced by the network effects of the Internet. Viral marketing is a marketing phenomenon that facilitates and encourages people to pass along a marketing message voluntarily. Viral promotions may take the form of funny video clips, interactive Flash games, advergames, images, or even SMS text messages.

It is claimed that a satisfied customer tells an average of three people about a product or service he/she likes, and eleven people about a product or service which he/she did not like. Viral marketing is based on this natural human behaviour.

The term "viral marketing" is also sometimes used pejoratively, to refer to stealth marketing campaigns - the use of varied kinds of astroturfing both online and offline to create the impression of spontaneous word of mouth enthusiasm.

History

Some argue the term viral marketing was originally invented by Tim Draper and coined by venture capitalist Steve Jurvetson of Draper Fisher Jurvetson in 1997 to describe Hotmail's e-mail practice of appending advertising for themselves to outgoing mail from their users.[citation needed].

The first to write about viral marketing was media critic Douglas Rushkoff in his 1994 book Media Virus. The assumption is that if such an advertisement reaches a "susceptible" user, that user will become "infected" (i.e., sign up for an account) and can then go on to infect other susceptible users. As long as each infected user sends mail to more than one susceptible user on average (i.e., the basic reproductive rate is greater than one), standard in epidemiology imply that the number of infected users will grow according to a logistic curve, whose initial segment appears exponential.