Google v Chicoms

I'm confused about this latest kerfuffle between the Chinese govt. and Google. Did Google really convince itself that the Chicoms would not abuse them? I guess they had some sort of agreement whereby Google agreed to allow filtering (aka censorship) while the Chicoms promised not to crack Google's systems. I'm guessing the Chinese government's crackers have been hammering google.cn ever since it was launched. I guess Google only now is getting pissed off about it. Why now?