Glossary · Detection & reputation
Port scanning
Probing an address across many ports to find services that answer, which is how most public proxy lists are assembled in the first place.
Port scanning sends a connection attempt to a range of ports on an address and records which ones respond. For proxy lists specifically, a scanner looks for ports that answer like a proxy, confirms one forwards a test request, and publishes the address-and-port pair. It is the mechanical origin of nearly every free proxy you will find.
This is why one address can appear on a list dozens or thousands of times over, once per open port, and why the ports themselves cluster: scanners check the conventional proxy ports first, so those fill up fastest. It is also why so many published entries never actually work. A port can look open to a fast scan and still refuse a real proxy handshake, and lists that never test past the scan republish that noise.
The defensive side of the same technique matters too. Site operators and hosts scan their own ranges to find exactly these exposed services before someone else does, since an open proxy on your network is both a liability and an invitation.
How HProxy handles it
We record every address-and-port pair separately and run a real proxy handshake against each, not just a port probe, which is why our per-port pages can tell you how many of the addresses on a given port have ever genuinely answered rather than merely looked open.
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