It's easy to say that "it probably won't happen" today. But so much can happen to change the game in the future. Budget cuts to security, internal employees being "in" on the hack, etc.

And what happens when it actually gets hacked? Nothing. Nobody will come out and say "our bad we shouldn't have collected and stored all this sensitive data". Heck, you would be lucky if it's not used as evidence for why further pushes for massive surveillance is needed.

Then there is also the issue that even though the data might be stored with good intentions today, we don't know who is going to be in charge tomorrow, or after that. Whatever Obama promises only lasts until somebody else becomes president, who thinks that all this data that is already stored and ready, should be used in new interesting ways. The data doesn't even need to leak and be hacked for it to be misused, when the owners of the data are in constant flux.

I'm not sure why we should take for granted that the NSA has a better security story than other branches of government. I have not been impressed with any of the US government offices I've worked with at any level.

I would find it somewhat relieving to find out that the NSA is run better than the rest of the government, but I don't see any reason to believe that's the case. If anything, they are likely as over-confident and technically out-of-touch at the higher administrative levels as their peers.

So the question is what they could download before getting caught... each time....

Also another possible threat scenario would be a spearphishing attack that would plant a virus on the network which would slowly (in botnet fashion) access pieces and send it to China a little bit at a time, uncoordinated, many little connections inside the network.

Ask yourself, if you had unlimited funds, spies in the US, and so forth, how would you attack the NSA? Those resources make a sophisticated and successful largescale attack a lot more possible and feasible.