Spoiler questions, now that we've seen 'Tron Legacy'

Why does Clu go bad? What happened to Tron? Why is Cillian Murphy even in this movie?

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1. Where is “The Grid?” Disney released the original Tron in 1982, shortly after the introduction of personal computers. In the film, the Master Control Program beams Kevin Flynn (Jeff Bridges) onto “The Grid,” a cyberspace realm that seemed localized on the computer mainframe of sinister corporation Encom. The sequel Tron Legacy has a contemporary setting, when everyone’s plugged into the world wide web. But when Kevin’s son Sam (Garrett Hedlund) gets downloaded onto The Grid, it looks conceptually the same as it did thirty years ago. Is it still the "Encom grid?" Is it on his father's personal mainframe? Does it have any connection to the current global network of Ebay and Facebook and on-line banking? Apart from the improved special effects, The Grid doesn't look very different.