I don't really like the word 'viral' - particularly when it's used to describe internet teaser campaigns for films. I have to admit, it's far easier to just say 'viral' campaign, and it does give a pretty accurate description of the technique that this method of advertising makes use of. But, it also conjures up images of tiny germs squirming around together in Petri dishes, people coughing on each other on buses, and red-eyed zombies chasing after Cillian Murphy.
However, the teaser campaign for Ridley Scott's Prometheus has been so good that I'm willing to call it plague-inducing if that's what the people want. Just take a look at these two videos; above is the recently released advert for 'David', the token android (played by the great Michael Fassbender). I particularly like the bit that has him 'wake up' covered in styrofoam, and the tiny Weyland Industries symbol incorporated into his fingerprint.
Below is the fictional TEDTalk that was created for the movie; this was the first of its kind - a collaboration between the creators of the TEDTalk and the filmmakers (in fact, it was directed by Ridley Scott's son). It features Guy Pearce in his role as Peter Weyland, head of the corrupt Weyland Corporation (presumably before it merged with Yutani) which, it appears, has been involved in the Alien saga from the very beginning. He outlines his vision for the future to a stadium of listeners - it all sounds very inspiring, but somehow you just know it's not going to wash in the end...
Even without these extras, the ad campaign for Prometheus was already exceptional - the trailer (which you can watch below) is so nail-bitingly frightening that it makes shivers run down your spine - if the advertising alone is this brilliant, what's the film itself going to be like? It'll either have people running screaming out of the theatre, or glued to their seats in a catatonic state of pure and absolute terror. Either one is box office gold.