I am building a new site, but creating the content using a subdirectory on an existing site. I have never posted a link to this subdirectory anywhere, yet searching Google reveals that Google has found these pages on my site and indexed them.
Further, I updated the site with a robots.txt file that WMT reports as being read, and testing the blocked pages using the WMT test tool indicates that the pages will not be indexed. Apparently this does not remove the pages from existing results, though I submitted a request to do so.
How did Google find these pages to begin with? Is it because I used a common subdirectory name and Google guesses at common subdirectories?