Curiosity about my referrers

Would anybody care to explain the "Not Your Business!" that's appearing on my referer page? Is that an anonymizing proxy, Opera, or something?

I don't mind of course, but I would like to observe for the benefit of who ever is doing that that right now, my referers page is all the feedback I get about this site; I do not have access to the web logs or anything else like that, so if it doesn't show on the referer page, I don't know about it. (In theory, a thousand people could be loading my site from their bookmarks every day, with no referrer, and I'd never know.)