The U.S. Marine Corps banned use of social web sites such as Twitter, MySpace and Facebook on its networks, citing security risks, while the Pentagon also said it will consider implementing similar bans.

These Internet sites in general are a proven haven for malicious actors and content and are particularly high risk due to information exposure, user-generated content and targeting by adversaries, the Marine Corps said in an order posted on its website.

 The very nature of social-networking sites creates a larger attack and exploitation window, exposes unnecessary information to adversaries and provides an easy conduit for information leakage, heightening security risks

The ban, authorized by Brig. Gen. G.J. Allen, the Corps’ chief information officer, does allow for special waivers for access if usage of the sites is mission critical.

The Defense Department meanwhile confirmed it was carrying out a formal review of its policies on the use of social networking sites.

In a July 31 memo, the deputy secretary of defense, William Lynn, said he had asked the Pentagon's chief information officer to draw up policy options examining the threats and benefits of so-called Web 2.0 capabilities.

Military bosses are concerned about viruses and other malware that can infect computers connected to such sites and then spread throughout a network. They also fear inadvertent release of information that could compromise operations and security.