Apparently the conventional wisdom (i.e., my reading of the NYTimes today) is the State Department cables now in the news can be traced to Mr. Manning, the private who's accused of also providing a bunch of military documents to Wikileaks. And how was a lowly private in intelligence able to access both military and diplomatic material? The answer seems to be after 9/11, in line with the recommendations of the 9/11 commission, there was a drive to knock down walls between bureaucratic silos. In additon, State Department managers saw an opportunity to kill two birds with one stone: by piggybacking on an existing secure intranet developed by the military they could save the costs in time and money of developing their own system (State was still stuck in a pre-Internet world with their cables) and get brownie points for sharing information.
Seems to me this doesn't show we should maintain silos and stovepipes; what it shows is good system designs need to track users and usage of data. If my credit card company is smart enough to know when my usage is different than my historical average, and to call me it on, then government databases should know what sort of usage pattern is expected from a given job position and to raise red flags when it changes.