One of my favorite viral marketing campaigns to date is one by Warner Bros for the release of The Dark Knight. The site Why So Serious? (www.whysoserious.com) was launched in an attempt to grab interest from the audience and make them earn the information. This is a peculiar attempt at marketing, as it uses a degree of reverse psychology: instead of trying to make their efforts and campaign content widely available anywhere, instead they made it exclusive to those who would devote the time to investigate it.
