[driftpower]

well, you could block x port from y connections. For example, proxies that have open port 9595 or 80 or 8080, you could do a scanner and if X connection ip(ex. 213.138.232.12) has X port open, then filter it. If it's Linux the system you are using for the server, i recomend you to use Iptables(firewall).

Good luck.