The Pentagon said soldiers will be allowed to Tweet, blog and update their Facebook pages on the US military's non-classified computer network under a new policy.
The decision came after a seven-month review with senior officials concluding that the benefits of social media outweighed the risks associated with free-wheeling web 2.0 sites that are popular with a younger generation of soldiers and Defense Department civilians.
Previously, the Pentagon worried that YouTube or other social media could take up precious bandwidth or that careless entries could expose military secrets.
While stressing the principle of allowing access, the policy unveiled Friday sets limits that grant commanders authority to "defend against malicious activity" such as cyber attacks and to bar access to sites with pornography, gambling or hate-crime content.
Commanders can also block access to social networking sites if necessary to protect a mission or protect sufficient bandwidth -- but only on a temporary basis, said the policy memorandum.
"This directive recognizes the importance of balancing appropriate security measures while maximizing the capabilities afforded by 21st Century Internet tools," Deputy Defense Secretary William Lynn said in a statement.
Social networking sites and other Internet services have "become integral tools for operating and collaborating across" the Defense Department and with the public, it said.
The policy requires consistent rules across the military, as restrictions had varied widely across offices and branches of the armed forces.
The US Marine Corps in August had renewed a ban on Twitter and other social networking sites, while the Army had been moving to ease some restrictions though maintained a list of banned social media sites.
Officials said the Marines would have to loosen the rules they had imposed and bring their guidelines into line with the new policy.
Defense officials and senior officers have increasingly recognized social media as crucial to reaching a younger generation, both within the ranks of the military and the wider public.
The top-ranking US military officer, Admiral Mike Mullen, has a large following on his Twitter account and for many military families, Facebook has become a vital link to loved ones deployed abroad.
The Pentagon first announced the policy change on Friday via the Twitter feed of Price Floyd, the principal deputy assistant secretary of defense for public affairs.
Explore further: Erdogan passes law tightening Turkey's grip on Internet