Platte River was probably selected on the basis of being worthless, ignorant and insignificant peons that could serve as an unwitting scapegoat without having to sacrifice a loyal servant or damage any political connections. Note the timeline - it was way after anything significant was done on that email system.
How would they know Platte River was secure?
FLASHBACK:
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Special Report with Brit Hume [Fox News] (USA) - December 10, 2008
HUME: The recent cyber-attack on Pentagon computers has been linked to former intelligence operatives from a foreign country. National security correspondent Jennifer Griffin joins us live from the Pentagon with details — Jennifer.
JENNIFER GRIFFIN, FOX NEWS NATIONAL SECURITY CORRESPONDENT: Brit, FOX News has learned that the cyber-attack on the U.S. military’s classified information network has been traced to a front company run by former Russian FSB or KGB spies. The attack, you’ll remember, led the Pentagon to ban the use of all thumb drives because that is how the worm got into the classified military network.
One official said the worm managed to not only map classified military files but may still be in the system waiting to send files back, change information needed by commanders or destroy the system at a later time. The intrusion was discovered, we’ve learned, by the U.S. military in Afghanistan.
The attack came through the local Internet service provider which the Afghans, under U.S. supervision, contracted out to this front company run by former Russian spies. The U.S. military relies on this Internet service provider. Today, Michael Chertoff warned the Russians had already used cyber warfare in Georgia.