There's a security restriction called "ITAR". ITAR stands for "International Traffic in Arms Regulations". This is a body of information that carries no security classification. However it is not permitted for this information to be passed to foreign governments or corporations. If a civil servant or government contractor releases ITAR information then that person is in trouble with the US government (fine or imprisonment). The ITAR classification could be put on almost anything including publicly known Marquardt data. A fair amount of declassified NASA and Air Force technical resports have been reclassifed as ITAR restricted documents. The guy who produced that website probably revealed ITAR data concerning ramjet specifications (I say that's a safe bet). I've seen other "interesting" websites with aerospace related data suddenly go offline. I suspect those folks also had phone calls from the FBI. Google "ITAR" if you want to learn more.

Gary