* Proxy checkers such as Charon can filter by IP ranges.
* The AccessDiver proxy checker has an option to remove CoDeeN/PlanetLab proxies using the port.
(Also, IP / Proxy List Formatter | CoDeeN Filter | Batch IP to Country Lookup - [IPMaster.org] filters CoDeeN (probably by port or IP).

These methods seem blunt and insufficient.
* CoDeeN IP's are probably changed from time to time (added,removed).
* Some non-CoDeeN proxies use some CoDeeN ports.
* There are proxy "nasties" other than CoDeeN (DansGuardian, SurfControl, NetSweeper, Barracuda, etc.)

AccessDiver has an option to test proxies against a site (Charon also?). In theory, this seems to be a better way. However, a simple test run against amkingdom (for which I assumed CoDeeN,etc. would disallow access) was completely disappointing, not appearing to filter much, if anything.

(amkingdom was chosen because it is fast and popular - proxies that do filtering will almost certainly filter this).

I then wrote a little test program to independently test this concept: cycle through ~2000 proxies leached by FPL, executing http connections (HEAD, 12s timeout) to amkingdom, and checking the response to see if the target has been reached. This only returned about 10 "valid" proxies. This can't be right, can it?

Yet another method, used by "On Cracking Rampage" and CyberWaper, is to test the response against "proxy block phrases" such as "CoDeeN" and "DansGuardian".

These methods appear to be sound.
Or am I overlooking something?
Is there any working implementation of these methods for filtering proxies?
If not, is there any source code available (preferably java) for proxy checking that can be adapted?


References:
G-Lock Software • View topic - Planetlab/Codeen Exclusion List
http://forum.my-proxy.com/suggestion...s-t256.15.html
http://forum.my-proxy.com/proxy-ques...s-t3381.0.html