That would be the Phillipino inmates
No, not that one. My bad. They are called flash mobs. Done in Paris, Canada, Taipei and a few other countries (one had over 13,000 people). And they weren't inmates!! A great one was the mass mob for Black Eyed Peas doing I've Got a Feeling. One girl starts it off:
http://www.youtube.com/watch?v=1aSbKvm_mKA