Describing traffic to the services as "recreational", General Burwell Baxter Bell informed troops that it "impacts our official DoD network and bandwidth availability, while posing a significant operational security challenge".
The ban does not affect home computers that access the internet through public internet providers.
But because such services are not available in most parts of Iraq and Afghanistan, the ban effectively limits the ways that servicemen can communicate with friends and family at home.
Videos from the front lines have sparked debate on both sides of the conflict. One video, for instance, shows a truck getting hit by a rock, prompting the movie maker to complain that they are not allowed to shoot at the children throwing the rocks.
The video prompted calls supporting the war, as well as for the US to pull out of Iraq.
Critics have charged that the ban is aimed at containing such user-generated content that could further undermine support for the war.
General Bell also warned users of home computers not to forward links or files to systems on the Army network. "To do so would compromise operational security and create an opportunity for hacking and virus intrusion," he stated.
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