Page cloaking can broadly be defined as a technique used to deliver different web pages under different circumstances. There are two primary reasons that people use page cloaking:

i) It allows them to create a separate optimized page for each search engine and another page which is aesthetically pleasing and designed for their human visitors. When a search engine spider visits a site, the page which has been optimized for that search engine is delivered to it. When a human visits a site, the page which was designed for the human visitors is shown. The primary benefit of doing this is that the human visitors don't need to be shown the pages which have been optimized for the search engines, because the pages which are meant for the search engines may not be aesthetically pleasing, and may contain an over-repetition of keywords.

ii) It allows them to hide the source code of the optimized pages that they have created, and hence prevents their competitors from being able to copy the source code.

Page cloaking is implemented by using some specialized cloaking scripts. A cloaking script is installed on the server, which detects whether it is a search engine or a human being that is requesting a page. If a search engine is requesting a page, the cloaking script delivers the page which has been optimized for that search engine. If a human being is requesting the page, the cloaking script delivers the page which has been designed for humans.

There are two primary ways by which the cloaking script can detect whether a search engine or a human being is visiting a site:

i) The first and simplest way is by checking the User-Agent variable. Each time anyone (be it a search engine spider or a browser being operated by a human) requests a page from a site, it reports an User-Agent name to the site. Generally, if a search engine spider requests a page, the User-Agent variable contains the name of the search engine. Hence, if the cloaking script detects that the User-Agent variable contains a name of a search engine, it delivers the page which has been optimized for that search engine. If the cloaking script does not detect the name of a search engine in the User-Agent variable, it assumes that the request has been made by a human being and delivers the page which was designed for human beings.

However, while this is the simplest way to implement a cloaking script, it is also the least safe. It is pretty easy to fake the User-Agent variable, and hence, someone who wants to see the optimized pages that are being delivered to different search engines can easily do so.

ii) The second and more complicated way is to use I.P. (Internet Protocol) based cloaking. This involves the use of an I.P. database which contains a list of the I.P. addresses of all known search engine spiders. When a visitor (a search engine or a human) requests a page, the cloaking script checks the I.P. address of the visitor. If the I.P. address is present in the I.P. database, the cloaking script knows that the visitor is a search engine and delivers the page optimized for that search engine. If the I.P. address is not present in the I.P. database, the cloaking script assumes that a human has requested the page, and delivers the page which is meant for human visitors.

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