YouPorn is a German online video sharing platform, similar to YouTube, that provides instant access to a huge collection of pornographic clips. Although there is no official reason, the service was removed from the German side of Google and it's not displayed in the results when you're searching the Internet with or without the SafeSearch function provided by the search technology. This problem, reported by Philipp Lenssen from Google Blogoscoped, follows the recently imposed self-censorship of Yahoo's Flickr, a service that blocked most of the adult images published on the photo sharing service and available to Germans.
As the same source reports, a Wikipedia article states that Google Germany removed YouPorn from the search results, saying that the country's authorities requested them to do so. "Google Deutschland (Google Germany) has eliminated YouPorn from their search results and replaced it with a link to Chilling Effects, claiming that "German regulatory body reported illegal material". Because the site itself is still accessible from Germany and the other Google versions in German language still list YouPorn, Google Germany's action has been sarcastically commented upon in a large number of blogs," the Wikipedia article states.
As usual, the Mountain View company replaced the results with a notification that informs the users about the removal and redirects them to the official page of ChillingEffects. "In response to a legal request submitted to Google, we have removed 5 result(s) from this page. If you wish, you may read more about the request at ChillingEffects.org," it is mentioned on the SERP.
Obviously, the removal of the pornographic website from the results is a little bit weird because the company didn't make it clear why they took this decision. However, apart from the demands of the German authorities, there might be another reason: the similarities between YouTube and YouPorn, two services which share numerous similar features.