This is The Dark Knight Viral “Why So Serious?” Case Study. The “Why So Serious?” campaign won the Cannes 2009 Cyber Grand Prix in the viral category. It was a huge global success, with over 10 million unique players participating! It was created by 42 Entertainment.

Source:
http://www.digitalbuzzblog.com/the-dark-knight-viral-why-so-serious-case-study/