per a BBC post:
http://news.bbc.co.uk/2/hi/americas/6655153.stm
"The US military is blocking troops from using certain websites for sharing photos, video clips and messages ... The US says the use is taking up too much bandwidth and slows down the military's computer system. But a US Strategic Command spokesman said a "secondary benefit" was to help operational security."
Things are different when there's a war on, and the US is currently fighting three.

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