A proxy blocker is a software application that prevents users on a computer network from accessing proxy sites that subvert website filtering rules the network administrator has put in place. Many enterprise web-filtering solutions now include proxy blocking as part of their security package. Website filtering software blocks users from accessing certain domains like social networking sites or video streaming portals. Some users, however, bypass these restrictions by using proxies, websites that provide an indirect, anonymous connection between a client and a web server. Proxy blockers deny access to these proxies using a number of techniques, most of which need to be regularly updated.
Computer administrators, particularly those in charge of workplace or corporate networks, may restrict users of their network from accessing certain sites for a number of internal reasons. Social networking sites are known to reduce productivity; usage of other sites may damage the reputation of the firm that the computer network belongs to. Network administrators restrict sites by maintaining a centralized list of disallowed sites. Any attempt to access these sites from a client browser within the network will be thwarted and, in some cases, a record of the infraction will be made. Before long, however, users realized that they could use proxy servers to get around network restrictions.
Proxy blocker technology works both ways though, and users can often implement other proxy websites to circumvent the original barriers that were put in place. For example, if a television network placed a proxy blocker on anyone outside of their normal viewing area, only local residents would be able to access its content. Someone from that jurisdiction may have set up their computer to work as a proxy for others, however, so users would connect to that proxy and then access the local content from afar. It tricks the proxy blocker into thinking that the visitor is someone that they're really not, so the proxy is defeated by using another proxy.
The average proxy blocker works on a very simple principal; administrators simply add proxy sites to the list of restricted websites. Their problem, however, is that hundreds of proxies are created every day. A new development is peer-to-peer proxies, software that turns a normal, household computer into a proxy server that can be used to surf restricted parts of the Internet. Proxy blocker developers have to constantly update their lists of restricted sites, a task that typically requires significant amounts of overhead. More sophisticated methods of preventing users from accessing specific sites are to block file types instead of domains; for example, a video-streaming site may be accessible on a computer network, but the videos will be restricted from loading.