Cloaking is a form of black hat SEO manipulation in which the content presented to the search engine spider is different from that presented to the users' browser; this is done by delivering content based on the IP addresses or the User-Agent HTTP header of whatever is requesting the page. The only legitimate uses for cloaking used to be for delivering content to users that search engines couldn't parse, like Adobe Flash. However, 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 content. For this reason some search engines are banning sites using cloaking.

In more recent times several well known and well respected sites have taken up cloaking to deliver personalized content to their regular customers. In fact, many of the top 1000 sites - including household names like Amazon - actively cloak. None of these have been banned from search engines purely because of cloaking.

Increasingly, for a page without natural popularity due to compelling or rewarding content to rank well in the search engines, Webmasters must 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 end users to consume. As such, cloaking is an important technique to allow Webmasters to split their efforts and separately target the search engine spiders and end users. As with anything, this technique can be used responsibly, or less so.

Cloaking and IP Delivery

There is a fundamental distinction between cloaking and IP delivery. With cloaking, search engines and people never see the other's pages, whereas, with other uses of IP delivery, both search engines and people see the same pages. One use of IP delivery is to determine the requester's location, and deliver content accordingly. It is IP delivery, but it isn't cloaking. Google does this when delivering their AdWords and AdSense advertisements. Cloaking delivers different pages to the search engines than to people, and each never sees the other's pages.

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