What is a Proxy?

In computer networks, a proxy server is a server (a computer system or an application program) which services the requests of its clients by forwarding requests to other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server. The proxy server provides the resource by connecting to the specified server and requesting the service on behalf of the client. A proxy server may optionally alter the client's request or the server's response, and sometimes it may serve the request without contacting the specified server. In this case, it would 'cache' the first request to the remote server, so it could save the information for later, and make everything as fast as possible.

A proxy server that passes all requests and replies unmodified is usually called a gateway or sometimes tunneling proxy.

A proxy server can be placed in the user's local computer or at specific key points between the user and the destination servers or the Internet.

Proxies that focus on WWW traffic are called web proxy. Many web proxies attempt to block offensive web content. Another purpose is to serve as a web cache. Some web proxies reformat web pages for a specific purpose or audience (e.g., cell phones and PDAs)

Some proxy servers implement a logon requirement. In large organizations, authorized users must log on to gain access to the web. The organization can thereby track usage to individuals.

Proxies can also be installed by online criminals, in order to eavesdrop upon the dataflow between the client machine and the web. All accessed pages, as well as all forms submitted, can be captured and analyzed by the proxy operator. For this reason, passwords to online services (such as webmail and banking) should be changed if an unauthorized proxy is detected.