Viral marketing is a form of marketing that has gained popularity in recent years.Viral marketing gets its name from its similarity to a virus. The point of viral marketing is to "infect" one person with your marketing idea, who will then spread the news to someone else, thereby "infecting" them. Those who engage in this type of marketing hope to reach as many people as possible, basically through word of mouth.

Viral marketing is based on the idea that if someone finds something interesting, they are likely to pass it on to their friends. Sometimes what is being passed does not appear to be advertising at all.

The earliest use of viral marketing is usually attributed to Hotmail, a web based email provider. When Hotmail was first starting out, they would attach advertising to the bottom of emails that were sent from their users. The idea was to have people sign up for Hotmail because they got the message from their friends.

There are many types of viral marketing. The most interesting is perhaps undercover viral marketing. Undercover marketing occurs when people do not know they are being marketed to. The goal is simply to create "buzz" or to have people talk about the products. An example would be having paid individuals post in chat rooms or message boards regarding a particular product or idea. Sony Ericsson is known for a viral marketing scheme where they sent out paid actors who asked people to take their picture. The actors would talk to the person about their camera and how great it was.

Other types of viral marketing include alternate reality games (ARGs). ARGs are games which blur the line between fiction and reality. ARGs are especially interesting because they involve real life people interacting with "fake" characters who exist in the "real" world. There are often clues given, items hidden to be found, puzzles to be solved, and things such as phone calls from "characters" in the game. Not all ARGs are viral marketing, but when done well, they can be hugely successful marketing strategies.

Viral marketing is very successful because it works to create a buzz about the product and then subtly encourages people to tell someone else. Because of this, the advertising doesn't have to reach the secondary user directly. The person initially "infected" by the viral marketing can "infect" many others with no additional work required on the part of the advertisers.