I got an email from a site in my space who said "WMT says you have 1600 links to my site and are indexing my content - please stop".
I had no idea what was going on, but it appears on my mobile subdomain (m.MyURL.com) that her site is getting indexed somehow. (A site:MyURL.com hersite.com shows all her pages indexed)
Where it gets really strange is that it also appears that any other website whose url ends with my domain string (RedMyURL.com, BlueMyURL.com) are ALSO being indexed on this mobile domain. But MyURLGreen.com is NOT indexed.
I use dudamobile for the mobile site - not sure if that matters, but perhaps there is some wildcard or screwup where it has decided to associate every URL that ends in myurl.com with my site?
Does you site have duplicate copies of the other site's pages (on your server)? If so, do these copy pages (on your site) appear in Google's search results if you search for exact text snippets in quotes? Does your site receive any traffic from Google to these pages. Does Webmaster Tools have any information about these pages?