What happened was the creators of the Dark Knight ARG made it looks like the Joker had hacked into everything! Took over websites, playing tricks on people, leaving cell phone numbers in baked cakes and having the cell phone baked into the cake, having the participants in the game follow the clues to solve the mystery...
To make a long story short: ARG's as defined by Wikipedia: An alternate reality game (ARG), is an interactive narrative that uses the real world as a platform, often involving multiple media and game elements, to tell a story that may be affected by participants' ideas or actions.
Here's another example of an ARG that took place a few years back:
http://www.thelostexperience.com/
This one promoted the coming of season three for Lost.
What all these ARG's have in common is that they are an innovative, fun and interactive way to not just market and advertise, let's say, an upcoming film or video game, but it incorporates different forms of digital media and technology. They use websites, cell phones, video cameras, etc...
I want to take this idea and make an ARG of some sort in the near or far future... Hmmm...