Couldn't resist the topic there.

I recently found a game by Introversion Software (who made Darwinia, which I believe was inspired by TRON in several aspects) called "Uplink". It was actually their first game, and it was released in 2001. The Demo is awesome, and contains many aspects of the full game. I'm not too sure what the limitations are.

The reason I put this in general disscusion is because:

A) Think of it as UserError.mod, but in real life
B) Perfect for Kevin Flynn/Jet Bradley wannabes
C) I've read that this movie contains references to movies about hacking. For example, at one point in the game, you hack a missile launch control computer, just like the kid in WarGames. I'm sure there's a reference to in there somewhere.

Official site