I apologize but there is no such thing as "it is (ALWAYS|NEVER) a good idea" no matter how many blog posts people wrote about that. It just depends on which ar

I apologize but there is no such thing as "it is (ALWAYS|NEVER) a good idea" no matter how many blog posts people wrote about that. It just depends on which are the tradeoffs between the antithetic goals that you have when you do any kind of security hardening. Aside from that, since many already mentioned port knocking as another layer in the pile of this game, let me point out that not all port knocking (-like) implementations are that weak, look e.g. at knockknock [ http://www.thoughtcrime.org/software/knockknock/ http://www.thoughtcrime.org/software/knockknock/ ].