Google won't give you the exact links that hurt you. I think if they did, then people would just disavow those specific links and go on spamming (hoping some other links would stick). Not really a lesson to learn there.

They do give you increasingly more information in Webmaster Tools about "unnatural links to your website": https://support.google.com/webmasters/answer/2700611?hl=en They task you to read the guidelines on linking: https://support.google.com/webmasters/answer/66356 and to apply your new-found knowledge to clear any suspicious links from your incoming links list. Then to kindly ask those other webmasters to remove those links (instead of spamming them for link requests). It is like a spammer rehabilitation program :). The spammer mindset is pretty cruel, selfish and destructive. You can't be too nice. That forms a pretty complex game theory with difficult opponents. Yet Google is somehow changing their opponents to clear up the spam they've created and cower in fear every time they announce an algorithmic update.