Oh I use the version that I found in this section here.
But I have got quite an idea now, I'll write a little checker myself.
It'll try to get a web page through the proxy and verify it. That should do the trick.
It will be quite slow as I don't know anything about writing programs with multithreading right now but the results will be 100% accurate.

I have got Version 5.50 that was posted in this board somewhere. I didn't apply any cracks so I thought it was for free...
I really like the way it checks http proxies because I can look at the judges answer and it seems to be very very accurate, even more than Charon.

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I am new to proxy scanning and checking so please tell me everything I could improve as I'm still learning!
Software I use at the moment:
Scanners:nmap, ProxyFire, my own scripts
Checkers: Charon, GPN