The man brought the Freedom Tower plans to the New York Post, which says the 150-page schematic is marked: "Secure Document - Confidential."
The documents are dated Oct. 5, 2007. They contain plans for each floor, the thickness of the concrete-core wall, and the location of air ducts, elevators, electrical systems and support columns.
The agency that owns the World Trade Center site, the Port Authority of New York and New Jersey, calls it a serious security lapse.
Spokeswoman Candace McAdams says mishandling the blueprints would be "cause for serious disciplinary action." But she says the plans are not detailed and have been updated several times since October.