Finally... a good viral thingymajig.

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.

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.