Viral marketing and viral advertising refer to marketing techniques that use pre-existing social networks to produce increases in brand awareness or to achieve other marketing objectives (such as product sales) through self-replicating viral processes, analogous to the spread of pathological and computer viruses. It can be word-of-mouth delivered or enhanced by the network effects of the Internet. Viral promotions may take the form of video clips, interactive Flash games, advergames, ebooks, brandable software, images, or even text messages. The basic form of viral marketing is not infinitely sustainable. – Wikipedia