Bugtraq: Re: "Exploiting the XmlHttpRequest object in IE" - paper by Amit Klein

[anonymous () anonymous com]

Another way to spoof a Referer header using XMLHTTP is to do something like this:
xmlhttp.SetRequestHeader("Referer:", "http://some.referer.com";);

Note that the ':' after the Referer does the trick here.  If this is not present IE ignores this header.
Thanks!