Internet Information Services (IIS), returns a set of substatus codes with its 404 responses. The substatus codes take the form of decimal numbers appended to the 404 status code. The substatus codes are not officially recognized by IANA and are not returned by non-Microsoft servers. Substatus codes Microsoft's IIS 7.0, IIS 7.5, and IIS 8.0 servers define the following HTTP substatus codes to indicate a more specific cause of a 404 error: 404.0 – Not found. 404.1 – Site Not Found. 404.2 – ISAPI or CGI restriction. 404.3 – MIME type restriction. 404.4 – No handler configured. 404.5 – Denied by request filtering configuration. 404.6 – Verb denied. 404.7 – File extension denied. 404.8 – Hidden namespace. 404.9 – File attribute hidden. 404.10 – Request header too long. 404.11 – Request contains double escape sequence. 404.12 – Request contains high-bit characters. 404.13 – Content length too large. 404.14 – Request URL too long. 404.15 – Query string too long. 404.16 – DAV request sent to the static file handler. 404.17 – Dynamic content mapped to the static file handler via a wildcard MIME mapping. 404.18 – Query string sequence denied. 404.19 – Denied by filtering rule. 404.20 – Too Many URL Segments. Custom error pages Web servers can typically be configured to display a customised 404 error page, including a more natural description, the parent site's branding, and sometimes a site map, a search form or 404-page widget. The protocol level phrase, which is hidden from the user, is rarely customized. Internet Explorer, however, will not display custom pages unless they are larger than 512 bytes, opting instead to display a "friendly" error page. Google Chrome included similar functionality, where the 404 is replaced with alternative suggestions generated by Google algorithms, if the page is under 512 bytes in size. Another problem is that if the page does not provide a favicon, and a separate custom 404-page exists, extra traffic and longer loading times will be generated on every page view. Many organizations use 404 error pages as an opportunity to inject humor into what may otherwise be a serious website. For example, Metro UK shows a polar bear on a skateboard, and the web development agency Left Logic has a simple drawing program. During the 2015 UK general election campaign the main political parties all used their 404 pages to either take aim at political opponents or show relevant