opening a page only clicking a banner

[grigione]

i need a script php  that permit of opening a page only clicking on a banner placed on sites of other users

If users click on banner the page open, if user type url of page directly in browser don't open with phrase access denied or similar

i know that it's possible with $_SERVER['HTTP_REFERER'] but it can be easily spoofed

any alternative?

[adamsinfo]

You could create some kind of call back to the original site to prove that the click came from that original site. Without that possibility though, $_SERVER['HTTP_REFERER'] is your only option, and yes, it can be easily modified.