Variously known wthin the advertising industry as permission-based marketing, relationship marketing what we will refer to here as viral marketing, was a term coined, according to Clay Shirky in "The Toughest Virus of All "by Steve Jurvetson and Tim Draper in Nov. ’98, in an article entitled "Turning Customers into a Sales Force") to describe the astonishing success of Hotmail, which grew to 12 million subscribers 18 months after launch. The first to write about viral marketing within media critical circles was Douglas Rushkoff in his 1994 book Media Virus

In marketing, it is still a relatively new idea; however, its impacts have been significant. A successful meme allows marketers to bypass expensive and increasingly inefficient broadcast media channels by generating buzz in the digital space. This potentially allows marketers to spend a great deal more time and money on creating a quality product than on its distribution. Viral marketing is popular because of the ease of executing the marketing campaign, relative low-cost (compared to direct mail), good targeting, and the high and rapid response rate. The main strength of viral marketing is its ability to obtain a large number of interested people at a low cost.

The techniques of viral marketing seek to exploit pre-existing social networks to produce exponential increases in brand awareness, through viral processes similar to the spread of an epidemic. 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 results in epidemiology imply that the number of infected users will grow according to a logistic curve, whose initial segment appears exponential. If each user sends mail to more than one susceptible user then the campaign will in theory continue forever, or at least until all susceptible users have already received the message. Even if the message is not forwarded quite that often, the message might still be forwarded many more times than it was initially sent.