Big Brother :) (maybe OT)

I made a virtual stock exchange game (PHP + MySQL). The game is for academic (student) use, and the sign-up is free. That puts inherent problems. A player could try to cheat by creating dummy accounts to control the virtual market. The administrator has the possibility to analyze each operation made by each player. The IP and date of each operation are logged in. If a player uses dummy accounts, the admin can see that - when you see suspicious operations that originates from the same IP and are only a few minutes apart, you can draw an educated conclusion :)) The cheaters' accounts can easily be suspended. Now the technical problem: the students use the faculty's computers to connect to the game. That means a connection through a proxy, and $_SERVER['REMOTE_ADDR'] returns the proxy, not the actual workstation. Conclusion: the admin cannot be 100% sure if a suspect is a cheater or it is just a coincidence. What can I do to be better able to detect cheaters ? Can I extract information from HTTP headers using PHP so I uniquely identify a client's machine ? Or anything else ? -- Best regards, CiTro :) > A cynic is an idealist who has finally learned the truth.