From the people that admitted themselves. Also, let's not forget that Snowden managed to get all sorts of data they didn't even know he took until he went publi

From the people that admitted themselves. Also, let's not forget that Snowden managed to get all sorts of data they didn't even know he took until he went public with it - and they still don't know exactly what he took in full. How many actual spies could've done that and then sell that info? Even CIA admitted that there are a lot of people trying to become double agents at CIA, and that's just for people they find out about. It can probably happen at NSA, too, especially with 3rd party companies having access to that much data.