Google, and probably most of the other search engines, suppresses, on certain search terms, some or even all of the results of this search. The suppression might be a local one, affecting some countries or even all global searches for these terms.
This is what happens when the user sends a search request to Google. Not only does Google look into their databases but they also process this request internally before it is shown to the user.
The suppressed data can be still in their database but the pre-processing removes them from the search results. The same mechanism is also used when spam sites are filtered out for obvious reason.
The case of Chester provides us with an example of global suppression. If you search for the term “lesbian” on the site torkyarkisto.marhost.com (lesbian inurl:torkyarkisto.marhost.com) google presents us one page and states: Results 1 – 1 of about 2
This of course makes us think, hej, whats with the other page, why isn´t this one shown as well ?
A similar search on altavista presents us with 2 sites, the second site is the Chester page which was removed from googles search results.
Lets go on to local censorship. The following site is a good starting point if your interested in reading more about local censorships, go to cyber.law.harvard.edu for a detailed research on the topic.
You can also take a look directly at the researchers findings, they currently have a list of 113 sites that have been excluded from search results of Google France and Google Germany.
Make sure you visit this excellent site for more information: Seth Finkelstein’s Anticensorware Investigations – Censorware exposed

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[...] I´ve written a short article about google suppressing search results in some countries which did not seem to bother the public opinion in those countries and elsewhere. Recent news about google china censoring search results on the other hand seem to create more public discussion. Should western companies bow to countries like china that have a different view of freedom of opinion. [...]