For one of my websites, the "Links to your Site" section of GWT shows hundreds of spammy links. I didn't create these links myself, and didn't know they existed until I saw them in the lists.
Many of the these links appear to be on pages created by automated methods out of copies of Google's own search results. Some appear to be on parked pages. Some are on .cn (China) domains, often with dozens from the same domain. Some of the pages have sex-type ads.
Also, some of these links appear to be ephemeral, or even on pages that no longer exist. I get the impression that many of these pages are continuously being created by automated methods and then replaced by others after a few days. What purpose this serves isn't clear to me.
I hope that Google doesn't count these backlinks against my site and harm its rankings.
I thought that Google was fighting spam and auto-generated content, yet it collected hundreds of these spammy links and shows them in GWT.