Proxies are often used to increase security. If there is no
gateway between 2 networks, or the gateway is configured to block
certain types of traffic from crossing, a proxy server is often used
to allow otherwise blocked data to go out. Proxy servers each use either
the original protocol (in the case of HTTP), or a slight variant of
the original protocol (in the case of some other protocols) that encodes
the name of the site they are trying to contact. The proxy server then,
in turn, contacts the desired site, and acts as a go-between for data.
Sometimes proxies are used in other circumstances, such as HTTP proxies acting
as caches. These proxies cache popular websites, reducing the amount of overall
network traffic. Another example would be
Internet Junkbuster, a proxy that alters the content of the data to
block advertisements on webpages.