Viral videos: what are they?

Over 1 million visitors in less than a week. The latest instant hit in YouTube is, apparently, a promotional video for the movie Quarantine, to be released worldwide later this year. However, the video doesn't make any reference to the film; in fact, it looks like some ordinary shot made by someone who happened to have a camera in hand, so viewers have been wondering what the whole sequence is really all about. As it generates discussion and more questions, it is also passed on to more viewers, who in turn send it to more people. In a matter of days, it becomes a viral video.

But what is a viral video? How can they help sell an idea or a product? How is it different from other promotional materials? Watch this news story and find out.