According to the memorandum, members of military departments and all authorized users of the Non-classified Internet Protocol Router Network (NIPRNET) can now use the publicly accessible capabilities of various social networking and user-generated content sites, instant messaging, forums, and e-mail. This includes YouTube, Facebook, Twitter, MySpace, and others. Access to porn, gambling, or hate crime sites will remain restricted, however, and commanders can cut down on social media use if they feel the need to "preserve operations security."
In August of 2009, the US Marine Corps issued a policy of its own that banned the use of social media on the Marine Corps Enterprise Network (MCEN) due to malware concerns and "information exposure" to adversaries. It wasn't much of a surprise, either: security exploits are sprinkled throughout social networking sites, not to mention that fact that people just plain share too much. If IT admins are uneasy about the totally careless behavior of workers on social networking sites, the Marines undoubtedly had that much and more to worry about.
Of course, NIPRNET is separate from MCEN, but the Army’s Chief of Public Affairs advisor Lindy Kyzer told the New York Times that the new policy will indeed override the Marine Corps' current ban, as well as the Army's older ban on YouTube. All military units will need to open up access to social media sites, and any bans that take place must be temporary. "DoD is moving away from the silly notion of having ‘blacklisted’ social media sites and saying, ‘We’re not going to lay down the hammer and tell you where you can and cannot go, we’re going to mitigate risk as it comes,'" she said.
Source: Arstechnica.com