A proxy server is a client computer which acts as a server for other clients within its domain. It is a technique used to mediate communications from users to distant servers. Proxy servers often have caches, and store copies of documents retrieved by network users. If there is not a recent copy of the document in the server cache, the proxy server will send out for a new copy and forward this retrieved data to the user. In addition, when Internet connections are down, users may receive documents from the cache which are unretrievable during the down time.
Proxy servers can be a market researchers worst nightmare.
A hundred different clients could request the same document and the proxy server would only cause one hit to be recorded on the remote server. The obvious solution would be to try to gain access to the proxy server log. The outcome of proxy server caching to the log of a web server is to understate the number of users visiting the page. If the network served by a proxy is large, this underestimate can be substantial in size. With DNS, each computer, or network of computers, can be located by its IP address.