As Google writes in its autocomplete FAQ, “we exclude a narrow class of search queries related to pornography, violence, hate speech, and copyright infringement.”
“Autocomplete predictions are algorithmically determined based on a number of factors (including popularity of search terms) without any human intervention. Just like the web, the search queries presented may include silly or strange or surprising terms and phrases. While we always strive to reflect the diversity of content on the web (some good, some objectionable), we also apply a narrow set of removal policies for things like pornography, violence, hate speech, and terms that are frequently used to find content that infringes copyrights.
What words do Bing and Google censor from their suggestions? Read this article By Nicholas Diakopoulos