This section of U.S. Copyright law sets guidelines and restrictions for internet service providers and internet services which use their own servers to host user documents.  It allows for an internet service to continue functioning without fear of reprisal from copyright property owners so long as the operators of the service are not participating in the infringement and do not know of the infringing material’s existence on their servers.

    This governs server liability, stating “a service provider shall not be liable to any person for any claim based on the service provider's good faith disabling of access to, or removal of, material or activity claimed to be infringing or based on facts or circumstances from which infringing activity is apparent, regardless of whether the material or activity is ultimately determined to be infringing.”

    It is this kind of exemption that keeps sites like YouTube and BitTorrent search sites up and functional.  If the copyright owner actively complains, the server simply takes down the files and no legal issue is raised (meanwhile the copyrighted content likely pops up again within a matter of days).