Relax! The whole point of the system, as Checkboard says, is that it is 'fail-safe' in the event of such codes being compromised. Whilst I hope no-one would deliberately erode this final layer of security, it is just that: a layer. For terrorists to compromise the F/D through 'knowing' the codes an lot of unrelated failures have to have occurred, from the failure of government intelligence to the failure of F/D crew to follow SOPs. Whilst not impossible, please do not lose sleep over these things.
Frantic hyperbole about SECURITY SENSITIVE info and panicked requests to PLEASE DELETE THIS THREAD show that some people really have been frightened by the political rhetoric of the last 8 years. Before 11/9 I used to have passengers visit the flight deck during flights and stay in during TO and/or LDG. So there weren't nutters about then? (we know there were - FedEx). The fact is the risk is very, very small. Keep things in perspective and the paranoia to a minimum.
Sleep easy!