“Viral Marketing describes any strategy that encourages individuals to pass on a marketing message to others, creating the potential for exponential growth in the message's exposure and influence”

It's a relatively new marketing and advertising tool that more and more companies are taking note of. Viral marketing comes from the idea of a computer virus, each user spreads it on to other users who in turn spread it further. It multiplies and people notice it and pay attention.
Viral Marketing can take place on a number of platforms, from videos and animations to flash games and websites. The internet has played a crucial role in viral marketing. Websites such as YouTube allow companies to post videos which will reach a broad audience, and social networking websites allow users to post the links to the videos or websites for their friends to see.

Although companies may pump millions into their marketing campaigns, it does not mean the campaign will go viral. Viral marketing only works if people catch on. For example, Old Spice has one of the most successful viral marketing campaigns ever. ”The man your man could smell like” started with a YouTube video and can now be seen on TV. Microsoft attempted to acheieve the same success for their Windows 7 phone and even recruited the same actor, Isaiah Mustafa, from the Old Spice video but that marketing campaign didn't go viral.
Another example of Viral Marketing was the film “Cloverfield” Trailers depicting the head of the statue of liberty crashing to the ground were shown before films in cinemas, followed by a date. There was no name or other information given. This garnered a lot of intrigue for the film and people actively searched for information on it.