Google changed their robots.txt and included entries for finance, extern_js and MBD.
Old robots : 126.96.36.199/search?q=cache:4 ...
New robots : www.google.com/robots.txt
It's weird to see that www.google.com/mbd resolves correctly. Google actually serves a blank page.
What could mean MBD? Maybe "million barrels per day", or "minimal brain dysfunction"? Don't think so. Maybe Google Embed, a service that lets you create mashups using Google services.
Update: Peter Dawson suggests in Blogoscoped Forum that the acronym may mean "medical and biological database".