A document describing efforts to bomb-proof a new Pentagon annex in Alexandria was posted on a public government Web site, according to Reuters.

The 30-page plan details structural design features, which are aimed at thwarting an attack on the Mark Center office complex. Around 6,400 Defense Department personnel are slated to move into the facility later this year.

The document, which has since been removed from the Web, was posted on a site maintained by the Army Corps of Engineers, Reuters reported. Experts quoted in the story said the plan is a “recipe for an attack” and would allow terrorists to potentially find weaknesses in the building’s design.

“This should not have happened. We take it seriously, ” said Ken Wells, a spokesman for the Corps, in an interview with Reuters.

Some experts said the document also raised questions about the building’s level of bomb resistance. Recent attacks, including the 1993 World Trade Center bombing and a 1995 attack on an Oklahoma City federal building, used far larger quantities of explosives than the Mark Center is designed to resist, according to the report.