Marines can no longer use Facebook or Twitter, two of the most popular Internet social networking Web sites. "These Internet sites in general are a proven haven for malicious actors," and "are particularly high risk due to information exposure, user-generated content, and targeting by adversaries," the Marine Corps stated in MARADMIN 458/09, issued Aug. 4. Under certain circumstances, such as mission-critical necessity, Marines can seek waivers to the new regulation.