ActionScript Protection/Encryption

Hi!
Lets say that I have a flash interface that uses php to write/read vars.
So if someone wants to hack our website all he has to do is look at the code and send some vars manually to the .php file.

I’ve seen some encryption apps that claim to fully protect your swf but at the same time there are those who claim to decompile protected ones.

Is there any better way to protect the php>flash communication?