This guest post is by Adam L. Penenberg, author of Viral Loop. Four months before my latest book hit store shelves, my publisher wanted to change the title. Viral Loop might be catchy, and reflect what the book is about—and isn't that what a title is supposed to do?—but Hyperion worried that some readers would be put off by the word "viral." Would they shrink away for fear it was about "swine flu"? The book looks at entrepreneurs who built multimillion- and in some case billion-dollar businesses from scratch by incorporating virality into their products and businesses. Many iconic companies of our time, including Facebook, Twitter, YouTube, eBay, PayPal, Flickr and rising stars like Twitter are prime examples of a “viral loop”—to use the product, you have a strong incentive to spread it. At some point, as the number of users doubles, then triples, the company achieves what's known as a "viral loop," when the product spreads even if the company does nothing to promote it. The trick is that they all created something people really want, so much so that their customers happily spread the word about their product for them. The result: Never before has there been the potential to create wealth this fast, on this scale, and starting with so little.