User blog comment:Night Fury/The unknown SPY/@comment-48285-20111219192910

I don't think Kalluto is the Spy here. I think it's somebody working for Pariston because he is the one that said to the person on the phone to report back to him about anything his campaign needs changed. And, as Torune said, Tsubone was being stalked by two people-meaning Hisoka and Illumi because they're after Killua and Alluka. So, it's unlikely that Kalluto is the spy because he isn't even a Hunter.