Cloaking is a black hat search engine optimization (SEO) technique in which the content presented to the search engine spider is different to that presented to the users’ browser. This is done by delivering content based on the IP addresses or the User-Agent HTTP header of the user requesting the page.
When a user is identified as a search engine spider, a server-side script delivers a different version of the web page, one that contains content not present on the visible page. The purpose of cloaking is to deceive search engines so they display the page when it would not otherwise be displayed.
As of 2006, better methods of accessibility, including progressive enhancement are available, so cloaking is not considered necessary. Cloaking is often used as a spamdexing technique, to try to trick search engines into giving the relevant site a higher ranking; it can also be used to trick search engine users into visiting a site based on the search engine description which site turns out to have substantially different, or even pornographic content.
For this reason, major search engines consider cloaking for deception to be a violation of their guidelines, and therefore, they delist sites when deceptive cloaking is reported.
Cloaking is a form of the doorway page technique.
The black hat perspective
Increasingly, for a page without natural popularity due to compelling or rewarding content to rank well in the search engines, webmasters may be tempted to design pages solely for the search engines. This results in pages with too many keywords and other factors that might be search engine “friendly”, but make the pages difficult for actual visitors to consume. As such, black hat SEO practitioners consider cloaking to be an important technique to allow webmasters to split their efforts and separately target the search engine spiders and human visitors.
Cloaking versus IP delivery
IP delivery can be considered a more benign variation of cloaking, where different content is served based upon the requester’s IP address. With cloaking, search engines and people never see the other’s pages, whereas, with other uses of IP delivery, both search engines and people can see the same pages. This technique is sometimes used by graphics-heavy sites that have little textual content for spiders to analyze.
One use of IP delivery is to determine the requestor’s location, and deliver content specifically written for that country. This use isn’t necessarily cloaking. For instance, Google uses IP delivery for AdWords and AdSense advertising programs in order to target users in different geographic locations.
As a mean of determining the language(s) in which to provide content, IP delivery is a crude and unreliable method; many countries and regions are multi-lingual, or the requestor may be a foreign national. A better method of content negotiation is to examine the client’s Accept-Language HTTP header.