I have seen some sites which provide a code box which members can put on their website. Now if we change the code it actually stops working. I am looking to create such code which people can have on their site but if you see on may they have some encrypted like string in such remote codes... what is the best way, I mean how this is achieved(the remote code). Is this some Javascript or what? Can I build such system using php. I know PHP tells the reffers using server variables but here intention is to make a remote code that a member can put on his or her site and also he or she can not change the code or use it on wrong place. Do I make sense?