The sites increase the risk of sensitive information leaking out to adversaries, the order explains.
The ban, which will last a year, essentially rules out use of all public social networks by Marines, unless a mission-critical need exists. The fully-capitalized document reads, in part:
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 VERY NATURE OF SNS CREATES A LARGER ATTACK AND EXPLOITATION WINDOW, EXPOSES UNNECESSARY INFORMATION TO ADVERSARIES AND PROVIDES AN EASY CONDUIT FOR INFORMATION LEAKAGE THAT PUTS OPSEC, COMSEC, PERSONNEL AND THE MCEN AT AN ELEVATED RISK OF COMPROMISE. EXAMPLES OF INTERNET SNS SITES INCLUDE FACEBOOK, MYSPACE, AND TWITTER.
That's not to say that the Department of Defence is turning its back on social media, however: a new DOD site with social media integration is expected to launch this month, writes Wired. Meanwhile, the Marine Corps Facebook page has more than 75,000 fans.