すべての403,400エラーを404エラーに変更するには、これを/etc/apache2/conf.d/localized-error-pagesの最後または.htaccessに配置します
# Will raise a 404 error, because the file <fake_file_for_apache_404.php> doesn't exist.
# We change 403 or 400 to 404 !
ErrorDocument 400 /fake_file_for_apache_404.php
ErrorDocument 403 /fake_file_for_apache_404.php
# We need to rewrite 404 error, else we will have "fake_file_for_apache_404.php not found"
ErrorDocument 404 "<!DOCTYPE HTML PUBLIC \"-//IETF//DTD HTML 2.0//EN\"><html><head><title>404 Not Found</title></head><body><h1>Not Found</h1><p>The requested URL <script type=\"text/javascript\">document.write(document.location.pathname);</script> was not found on this server.</p></body></html>"
ErrorDocument 500 "Server in update. Please comme back later."