The U.S. Department of Defense recently sent out a reminder to all uniformed, civilian, and contractor personnel that it is illegal for them to look at illegally leaked classified documents (like the recent NSA stuff or earlier wikileaks material), especially on computers at work (which are monitored more thoroughly than non-work computers and smart phones). This is all somewhat absurd but it’s also true that there has been less of this idiocy over the last decade.
The military has always had problems with the rapid and widespread availability of material on the Internet, especially if the stuff is classified. American military leaders were at first very hostile to a lot of new Internet capabilities. For example, until four years ago most American troops were banned from access to social networking sites. This was not just Facebook but also twitter, YouTube, and photo-sharing sites. Bowing to growing pressure from the troops, the military unblocked access to these sites. The block had meant that anyone using a computer connected to Department of Defense network (NIPRNET) was no longer able to reach the banned sites.
One reason for the ban was quite practical. All those video and audio clips were jamming up the network and making it difficult to get official business done. This was a problem university networks began to encounter in the 1990s, and solved by a combination of expanding capacity and restricting how much students could use the network for downloading large files. The Department of Defense was in a slightly different situation because many of its users overseas depend on satellites for their Internet connection. Land based fiber-optic lines can provide a lot more capacity but in combat zones like Iraq and Afghanistan, satellite was often all that's available.
But when the Internet was available the troops loved it, even in its diminished form. Aside from the obvious popularity of email and use of messaging systems, the Internet also provided access to social networking systems. These gradually became a popular way for American troops overseas to keep in touch with the folks back home and with each other. The ease-of-use that has made these sites so popular with civilians was equally attractive to troops who don't have much time to spend on the Internet. Most troops in Iraq and Afghanistan had access to the Internet, but often via the equivalent of a dial-up connection. So sites like Facebook and Twitter were convenient enough for troops to quickly post messages, pictures, and short videos.
The brass were never happy with all this social networking and reluctant to attempt another crackdown. The suspect troops can be hard to identify, if they want to be, and have proved to be very responsible when it comes to OPSEC (Operational Security, not giving out info that can help the enemy). The brass has also learned that taking away Internet access would cause a serious morale problem.
Facebook has been found to be extremely useful in maintaining morale, as it is a convenient way for troops overseas to remain connected to family and friends back home. Twitter has become popular with commanders and technical team leaders, for keeping in touch with their subordinates. The military adopted many of the measures universities developed to keep their young users from causing a bandwidth shortage.