pentagonIn this post-9/11, ultra-high security era, it is hard to believe that the bomb-proofing specs of a new Defense Department building in the DC area would be on public view. Then again, the Internet is a tough beast to manage.

Reuters reporters Mark Hosenball and Missy Ryan discovered the sensitive information about Mark Center — where 6,400 Defense Department personnel are scheduled to move later this year — on a public website maintained by the Army Corps of Engineers.

Out of concern for the security of personnel who will work there, Reuters is not disclosing most of the details in the 424-page document stamped “For Official Use Only.”

But Hosenball and Ryan found an alarming detail on Mark Center: It is designed to resist threats posed by vehicle bombs detonated outside the building’s security perimeter carrying the equivalent of 220 pounds of TNT. That is far less than the amount of explosive used in the 1993 bombing of New York’s World Trade Center and 1995 bombing of the Alfred Murrah Federal building in Oklahoma City.

A Corps spokesman said the public posting was a mistake and that the government was working to take it down. But he acknowledged that it might have been sitting there since the document’s date -2009. Little comfort to 6,400 employees.