Ralph Wilson offers the following definition of viral marketing:"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. Like viruses, such strategies take advantage of rapid multiplication to explode the message to thousands, to millions."

He then offers the following 6 principles of successful viral marketing:

1) Gives away valuable products or services
"Free" attracts attention. Only try to capitalize on the attention after you've gotten it

2) Provides for effortless transfer to others
Make your message or content easy to pass on to others. Short, direct, simple messages transmit better than long complex ones.

3) Scales easily from small to very large
Plan ahead to make sure you dont limit the spread of your message by not being able to handle a lot of people getting it

4) Exploits common motivations and behaviors
Greed, narcissism, and the desires to be cool, popular, loved, and understood

5) Utilizes existing communications networks
Most people have 8-12 close relationships, but know and interact with hundreds of people. Find a way to get your message into their exisitng communication channels.

6) Takes advantage of others' resources
Make other people want to put your content, product, or message on their own web page, social network profile, blog, or email signature. Make them want to be associated with it.