While I was playing around with some very odd security issues in Internet Explorer and Forefox, I ran accross an interesting thing that Internet Explorer exposes when it is giving certain error messages. Internet Explorer exposes a few images that allow you to see if the browser
Of course there are dozens of ways to do this but this is one I hadn’t seen before. There is another document other than res://shdoclc.dll/refresh.gif like res://shdoclc.dll/search.gif, res://shdoclc.dll/pagerror.gif, res://shdoclc.dll/back.gif and others, but you get the point. Any of them could be used to detect that the browser is Internet Explorer for targeted attacks or for simply knowing more information about the user beyond their user agent. This is yet another reason why I think users spoofing their user agent as Google to catch blackhat SEO is pretty ridiculous.