The U.S. Marines issued an "immediate ban" Monday on the use of social networking sites across the military branch's networks.

Members of the Marine Corps can no longer access such sites as Facebook, MySpace and Twitter from the branch's networks or through virtual private network connections, according to an order from the U.S. Strategic Command. The sites are being blocked due to concerns over targeted malware attacks and information disclosure.

"The very nature of (social networking sites) creates a larger attack and exploitation window, exposes unnecessary information to adversaries and provides and easy conduit for information leakage..." the order said.

Users who require special access may apply for a waiver.

But Ken Silva, CTO of VeriSign, said Tuesday that he questions such a blanket move, considering the value of social networking sites to communicate.

"I think this approach is the natural one that people would jump to, but it's not sustainable," he told SCMagazineUS.com. "It is the way people are communicating on the internet now. I'm not dismissing their concerns, but I think it has to be thought through. Quite frankly, educating the troops might be a better strategy than denying them access."

He added that technologies such as web gateway and data leakage prevention also could come in handy.

The Marine Corps enlists about 204,000 active duty members and 40,000 reservists.

The U.S. Department of Defense is considering its own measure, according to a statement emailed to SCMagazineUS.com on Monday. The department is currently evaluating its Web 2.0 policy, which may result in a decision to prohibit access to all social networking sites.

In May, all domestic Army directors of information management (DOIMs) were directed to unblock Facebook, Twitter, Delicious, Flickr, and Vimeo on all domestic, unclassified military local area networks. The Army order was made to “leverage social media sites as a medium to allow soldiers to ‘tell the Army story' and to facilitate the dissemination of strategic, unclassified information,” the order stated.

Other social networking sites remained banned on Army networks, including YouTube, Pandora, Photobucket, MySpace, and MTV.