I had suspected Kabuto would be the spy, but I never suspected he would be a double agent or that Orochimaru himself would show up. Thinking back on the 2nd season of Naruto, around episode 51 or thereabouts, during the 2nd Chuunin exam when Kabuto was told to retrieve Sasuke for Orochimaru, I recall Orochimaru having second thoughts after sending him. Seems to me he suspected Kabuto had ill intentions toward him, and was considering double crossing him. Well, apparently not so.