Viral marketing is any marketing technique that induces websites or users to pass on a marketing message to other sites or users, creating a potentially exponential growth in the message's visibility and effect. A popular example of successful viral marketing is Hotmail, a company now owned by Microsoft, that promoted its services and its own advertisers' messages in every user's email notes.

"Was reviewing some competitive data and thought this was pretty interesting. I ran a batch analysis on Ahrefs of competitors. See attached screenshot. With just 603 backlinks, Our site is ranking up there with sites with 2x, 3x, 10x the number of backlinks/unique ips. Guessing some of this authority is coming from the backlinks program and general good quality of those links. Hard to speculate but nice to see." Ben R.
According to a paper by Duncan Watts and colleagues entitled: "Everyone's an influencer",[66] the most common risk in viral marketing is that of the influencer not passing on the message, which can lead to the failure of the viral marketing campaign. A second risk is that the influencer modifies the content of the message. A third risk is that influencers pass on the wrong message. This can result from a misunderstanding or as a deliberate move.