And other social networking sites as the Pentagon weighed a similar prohibition over cybersecurity concerns. The Marines had already banned the use of social media on military networks but issued a more detailed order this week defining which sites were out of bounds and noting possible exceptions to the rule, a Marine Corps spokesman, Lieutenant Craig Thomas said. "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...