Can anyone think of ways to prevent users from registering to a .php page under certain proxies? What would a group of proxies have in similar that might not effect regular users? For example, if you use Your Freedom, and try to access a .php page, is there any common factor that could be used to keep them off that part of the website in particular?
I'm not looking for an answer like 'ban by IP' though. All of the IPs used by Your Freedom are from entirely different countries, and there are infinite ways to change the IP range.