In my opinion, it is very, very hard to fully sandbox a clever AI. It can find side channels, or it can turn innocuous stuff into computing device...
e.g: "Accidentally Turing complete" shows how things that were not intended to be computing devices are actually Turing complete. Including: Magic the gathering, the card game.
http://beza1e1.tuxen.de/articles/accidentally_turing_complet...