Google Analytics: New Visitors, Returning Visitors… Other?!

While taking a look at Google Analytics today, I came across something strange.  I entered the dates as far back as they would go until present day for one of Miklos’s sites, and a mysterious lone ranger turned up.

Neither new, nor returning?  How can that…?  Apparently the same has happened to others.  So who is this single visitor over the course of 2 years on a site that’s had tonnes of pageviews?  Is it the same visitor on every site?  Is it GoogleBot Himself (but then, wouldn’t GoogleBot not track himself)?

When I checked visitor history on this blog, however, there was no Mystery Visitor.  I guess GoogleBot is out.  So who could it be?

I’m interested to know from other bloggers: If you date Analytics as far back as it will let you, does the same kind of result turn up?