So I recently messed up one of my sites. Rankings fell considerably and I couldn't figure out why - until now.. I had created a subdomain forums.example.com as an experiment into creating a community forum around the site. I was using vanilla forum software (http://vanillaforums.org/) as it seemed like a great alternative to vbulletin etc. However, other things got in the way and I never finished the set up and left it alone for a while. Fast forward a few months and my rankings are dropping considerably and I'm losing number 1 long tail positions I've had for years, at first I had know idea why and put it down to an algo update. But by luck I looked at the backlinks to the entire root domain rather than just www. and found thousands of shitty links with Polish payday loans etc anchors all pointing to pages on the forums.example.com subdomain. What I have done is delete the entire subdomains files and directories, by mistake 301'd all urls to my main domain although they are now 403 or 500 errors. How should I approach the link cleanup? I'm 99% sure these links are the cause of the rank drops. Should I disavow all the links pointing to the forums subdomain? Should I claim the forums.example.com domain in webmaster tools to see what links Google is showing and only disavow those? Help very much appreciated!