bingbing - 12:15 pm on Sep 28, 2012 (gmt 0)
Lucy, the IIS server logs and my own logging captured the visits. As you say, a custom IP check pushes the user to 404 if their IP is not permitted. We have a catch-all file in the folder that is loaded upon all page requests.
So what is happening is that Bing is requesting valid URLs, which we still don't know how they are getting, and is then pushed a 404.
I'm just trying to find out how it knows parts of a file system that are not published anywhere. Also, Bing has requested totally different files, which are not even related (linked) to some of the URLs in question, so it has not even spidered these in order to find them. It's like Bing is psychic lol.