While writing my thesis I came across this quote I used in my BA thesis. I thought it was brilliant then, and I think it's brilliant now.
"The reality is that no agency can create viral marketing, this is the sole domain of the consumer. Viral marketing is what happens when a campaign works - when we allow their message to travel via our own super efficient conduits. Perhaps it is entertaining on its own terms, divorced from the message. Perhaps it is a game or a story, like I Love Bees or other ARGs, where we take ownership in it. What distinguishes this from Guerilla Marketing is that we are aware of the message. When we are not aware of the message, or when the agents of the message misrepresent themselves, we call this 'deception'."
- Penny Arcade