Only half? I never found another logical explanation for how it's sustained. But, as we know from the news, FBI does not have the keys to it's back door for even high profile cases. So it's probably really for national security level-stuff... Or held by some other nation.

Good point. What if we find out that it's someone like the Syrian Electronic Army that developed this and has now backdoored everyone! Could we have reasonably expected an announcement from the government telling us as such?