Search engines tries to access node editing links In my dblog occassionally I am seeing query coming probably from search engines for links as

http://mydomain.com/node/13130/delete?destination=node

I wonder how possibly search engine got idea to query that kind of links (of course those links are not exposed to anonymous users)

I have xml sitemap installed but no such links exists in the index

When I query google for that link, I see that link is present in index (of course clicking on that link leads to access denied page), and also shows 

A description for this result is not available because of this site's robots.txt
One possibility is that one or more logged-in users have Google Toolbar or something similar installed. I don't have it installed any more because I noticed when developing locally that every time I fetched a page in my browser the request was repeated by the toolbar, presumably sending it to Google. 

In my experience there is no such thing as a non-public URL as far as Google is concerned. Any URL can be listed for indexing and so crawlers may attempt to fetch it from time to time. I suspect other tools may record URLs in a similar manner.