[lucasjung]

>Hackability from the internet isn't the only relevant consideration here.

True, but it is the central issue in this thread: the documents in question were hacked from a non-classified network.

The scenarios you describe for people circumventing barriers between classified and unclassified systems for the sake of convenience sound quite plausible, until you consider the severe penalties for doing so. With that in mind, only incredibly foolhardy individuals would do so for the sake of mere convenience--a much more serious motivation would be required for most people. In a large enough organization, someone would most likely do it anyway, but it wouldn't be nearly common enough to leave "high security networks...sitting wide open."

Really, the only plausible scenario for significant leakage of classified information is deliberate espionage. I'm not sure why people keep citing Manning as setting some sort of precedent or revealing a previously unknown vulnerability, because this type of espionage has been going on since the beginning of recorded history, and probably even before that. It's the reason why access to classified information requires both a clearance and "need to know." When "need to know" rules are relaxed or ignored, it becomes relatively easy for people to take information that they have no business accessing and simply walk out of the building with it, whether it be hard-copies or soft-copies. This tends to go in cycles, with "need to know" rules gradually loosening until a major incident occurs, after which they are rapidly tightened, and then the whole process repeats. There was a rash of such incidents all at once in the mid-'80s: http://en.wikipedia.org/wiki/1985:_The_Year_of_the_Spy