A proxy filter, also known as a proxy server, is a machine or application that serves as a middleman between a client and a server. When a user accesses a server through a proxy, the server believes it is completing the requests of the proxy, not the actual user, so it shields the client from identification. Computer administrators that want to restrict access to certain sites within their computer networks often make extensive use of a proxy filter, but users that want to get around network restrictions also employ them. Other users of proxy filters include people that have limited access to the Internet or those who wish to access content from other regions.
Network administrators are often forced to place certain sites, like social networking sites and other online services that reduce workplace productivity, under restriction. They often do so by utilizing a proxy filter as a gateway between users of the corporate computer network and the outside world. The proxy server will have a list of keywords, domains and Internet protocol (IP) addresses that are disallowed so that any user that tries to access them is redirected to a warning page instead of the requested site. Some proxy servers have advanced filtering options that allow network administrators to block file types and similar sounding keywords as well.
Proxies act outside of the jurisdiction of web-filtering software; users can use proxies to access websites that would be otherwise restricted on the network. Many filtering solutions exclude proxy filter sites from their centralized list of restricted domains. The ones that include the websites that act as a proxy filter have to constantly update their restricted sites list to include the hundreds of proxy sites that are created every day on the Internet.
Corporate network administrators are not the only ones that use proxy filters to restrict users from accessing parts of the Internet. Some governments have been using the proxy filter concept for years to prevent their citizens from accessing parts of the Internet that they deem to be unpatriotic or contrary to official government ideology. Governments that resort to content blocking often employ far more sophisticated methods of web filtering than those used in commercial applications. There are equally sophisticated proxy filter solutions that can be used to enable citizens of such countries to access the Internet in its entirety.