[crazyhatfish]

Actually, I don't think they state that is the only way they find content. I've had plenty of sites with obscure domain names for development and they always seem to find their way on to Google some how.

I imagine in addition to public URLs they also use URLs entered into Chrome (which isn't that public) and since they host DNS they probably crawl domain names requested through them too.

Legally I'm not sure what they stand on to do that but they're big enough now so I guess they don't worry too much about that nowadays.