Anonymous proxy servers are web servers that connect to a third party website and retrieves files or other resources on behalf of a requesting client. All throughout the transaction, the proxy server shall identify itself as the one requesting the resource, thereby maintaining the anonymity of the requesting client.

Anonymous proxy servers are widely used for a variety of reasons:

oIP address masking (useful, for example, when accessing a site in the US that is accessible only to IP addresses in the US and the one who needs to get into the site is in China or to bypass an IP blacklist).

oHiding personal data from the website being visited, particularly for sites which are known to sniff and mine for visitor's information.

oUsers using proxies generally avoid being bombarded with spams and other Internet threats. Some sites drop not only cookies in your computer when you visit their sites, and that little snippet left in your computer could really do a lot of harms.

oMay provide faster retrieval of files, as most proxy servers store in their cache frequently requested files and any request is run through the cache. If the file is in the cache, it is immediately sent to the requesting client and the proxy server no longer connects to the third party website.

oAllows anonymous surfing, which is important for people whose special interests aren't exactly wholesome or tasteful

A proxy server can be setup in the user's local computer (with a program that hides/changes the IP) or at some points between the user and the destination server.