A proxy or a proxy server is a machine that sits between you and the destination you are trying to reach. It can serve two purposes: speed and filter.

Speed - You may already be using a proxy without knowing it. ISPs usually have transparent web proxies in place to improve browsing speeds for their customers. For NTL users, it looks like xxxx-cache-1.server.ntli.net where xxxx is the code for your area e.g. bagu or cmbg. If you wish to use a different one, you have to enter the name of the cache and the port it uses under the Connection Settings/LAN Setting page in your browser's Tools/Option or Tools/Internet Options menu. The port should be set to either 8080 or 80.

Filter - The other common use of proxies is content filtering. Most companies have proxies in place to stop their employees from accessing undesirable material from the internet. Parents can do the same to protect their children at home.

So what is an open proxy? The proxies that I've mentioned, i.e. ISPs and companies, can only be used by their respective customers/employees. People who are not using that particular ISP or work for that specific company cannot connect to their proxies. An open proxy is one which anyone can connect to whether by design or not.

For example, if you are outside the UK and you connect through an open proxy in the UK to Radio Five, you will be seen as coming from within the UK and therefore the radio stream will work for you.