http : //rigorousintuition.blogspot.co.uk/2005/01/michael-chertoff-and-sabotage-of-ptech.html [ 13 ] simulated tracks appearing on radar during 9/11 http : //shoestring911.blogspot.co.uk/2010/08/lets-get-rid-of-this-goddamn-sim-how.html [ 14 ] describes the concept of computers sharing data in only one direction due to security classification .