The RFC is specific that a 451 response does not indicate whether the resource exists but requests for it have been blocked, if the resource has been removed for legal reasons and no longer exists, or even if the resource has never existed, but any discussion of its topic has been legally forbidden (see injunction).[4] Some sites have previously returned HTTP 404 (missing) or similar if they are not legally permitted to disclose that the resource has been removed. It is used in England by some Internet service providers utilising the Internet Watch Foundation blacklist, returning a 404 message or another error message instead of showing a message indicating the site is blocked.[5][6]