I am building a PC and a BeagleBords ARM embedded for public use. They run Ubuntu 13.04 and manually assembled Linux respectively.
Is there a way to prevent them from being shut down on pressing Shutdown button (on case, not on keyboard)? Sure, I can do it in hardware. I just prefer software solutions.
If somebody can say for sure "this is impossible" it would be a useful answer too.

Result: Ok, I understood it. One can prevent shutdown on press, but not on long press. I will have to make hardware switch to plug off Power button when needed.