Open Proxy - Testing For Access From An Open Proxy

Testing For Access From An Open Proxy

Because proxies might be used to abuse, administrators have developed a number of ways to refuse service to open proxies. Many IRC networks automatically test client systems for known types of open proxy. Likewise, an e-mail server may be configured to automatically test e-mail senders for open proxies. As they are typically difficult to track, open proxies are especially useful to those seeking online anonymity, from political dissidents, to computer criminals, to people who simply require privacy because it is within their rights to do so. Some users are merely interested in anonymity for added security, hiding their identities from potentially malicious websites for instance, or on principle, to facilitate freedom of speech.

Groups of IRC and electronic mail operators run DNSBLs publishing lists of the IP addresses of known open proxies, such as AHBL, CBL, NJABL, and SORBS.

The ethics of automatically testing clients for open proxies are controversial. Some experts, such as Vernon Schryver, consider such testing to be "very bad form". Others consider the client to have solicited the scan by connecting to a server whose terms of service include testing.