AS3 PHP Secure?

Please bare with me, I’m just starting to work on web development.

I’m having trouble finding a decent document on AS3 and implementing PHP. I can only assume it’s secure but since there’s ways to decompile a flash site what’s to stop someone from pulling the code and grabbing all the info from the server? I would assume Adobe already fixed any kind of security problems but there’s no way I can submit a project that sends PHP client side even if people haven’t figured out how to decompile CS3 yet. (Once again forgive me if I’m off the mark. I just started to learn back end.)