Search engines such as Google's that link to sites in "good faith" fall under the safe harbor provisions of the Online Copyright Infringement Liability Limitation Act which is part of DMCA. If they remove links to infringing content after receiving a take down notice, they are not liable. Google removes links to infringing content when requested, provided that supporting evidence is supplied. However, it is sometimes difficult to judge whether or not certain sites are infringing and Google (and other search engines) will sometimes refuse to remove web pages from its index. To complicate matters there have been conflicting rulings from U.S. courts on whether simply linking to infringing content constitutes "contributory infringement" or not.