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.