Key_Master - 1:37 pm on Mar 19, 2012 (gmt 0)
Why do you think it's doing such a great job if you don't understand how it works? Your server has an IP address that responds to port 80, I presume?
A lot of people have port 80 open on their IP. Whether they operate a family web server, a media server of some type (gamers), or for home security. Maybe their coffee machine is connected to the net. Even if they don't operate a home server, their router might be configured to respond to port 80.
That piece of code will block a lot of innocent visitors and the payout for blocking proxies is very small. Most proxies don't even have port 80 open. Especially, the ones you need to be most worried about.