WHC Internet Marketing Guide
Viral Marketing
Anything you create that people will pass on or recommend to others so that it spreads without your continue efforts is considered "viral". This can include free eBooks, informative or entertaining videos, online services that advertise themselves as they're used, etc.
The standard example of viral marketing is Hotmail -- every message sent thought Hotmail includes a link to Hotmail at the bottom. So everyone who uses it is sending out advertisements for it.
To spread effectively, your product must have what's called a "viral exponent" greater than 1. In other words, each person who's exposed to it must, on average, spread it to more than one other person. Otherwise, it will stagnate or die. Even if every 100 people exposed to it spread it to only 101 other people, it will grow on its own faster and faster over time.
To make a product viral, people must have a strong incentive to share it. For example, I once published a free eBook that didn't spread well until I made it "brandable" with each persons affiliate links. Once people could earn affiliate commissions if someone they gave their branded copy to bought something from it, it spread much more quickly, and my sales increased.
I spent quite a bit of time looking for a free PDF-branding program, and never found one I was satisfied with. Eventually, I purchased ViralPDF, which I highly recommend.
* Amazon.com best sellers displayed using CaRP Evolution with expanding reviews powered by CaRP's "Expander" plugin.