Anopen proxy is a type ofproxy server that is accessible by anyInternet user.
Generally, a proxy server only allows users within a network group (i.e., aclosed proxy) tostore and forward Internet services such asDNS orweb pages to reduce and control thebandwidth used by the group. With an open proxy, however, any user on the Internet can use this forwarding service.
An anonymous open proxy is useful to those looking for online anonymity and privacy, as it can help users hide theirIP address from web servers since the server requests appear to originate from the proxy server. It makes it harder to reveal their identity and thereby helps preserve their perceived security while browsingthe web or using otherinternet services. Real anonymity and extensiveinternet security might not be achieved by this measure alone as website operators can useclient-side scripts to determine the browser's real IP address and the open proxy may be keeping logs of all connections. Open proxies also do not stoptracking cookies andfingerprinters from identifying users.[1]
Most publicVPNs work through open proxies.
It is possible for a computer to run as an open proxy server without the computer's owner knowing it. This can result from misconfiguration of proxy software running on the computer, or from infection withmalware (viruses,trojans orworms) designed for this purpose.[2] If it is caused by malware, the infected computer is known as azombie computer.
Because open proxies are often implicated in abuse, a number of methods have been developed to detect them and to refuse service to them.IRC networks with strict usage policies automatically test client systems for known types of open proxies.[3] Likewise, amail server may be configured to automatically test mail senders for open proxies, usingsoftware such as proxycheck.[4]
Groups of IRC and electronic mail operators runDNSBLs publishing lists of theIP addresses of known open proxies, such asAHBL,CBL,NJABL (till 2013), andSORBS (in operation since 2002). The AHBL discontinued public access in 2015.[5]