Disavow Links is the latest and probably one of the most important Google Tool in 2012.

If you’ve ever been caught up in linkspam, you may have seen a message in Webmaster Tools about “unnatural links” pointing to your site. We send you this message when we see evidence of paid links, link exchanges, or other link schemes that violate our quality guidelines. If you get this message, we recommend that you remove from the web as many spammy or low-quality links to your site as possible. This is the best approach because it addresses the problem at the root. By removing the bad links directly, you’re helping to prevent Google (and other search engines) from taking action again in the future. You’re also helping to protect your site’s image, since people will no longer find spammy links pointing to your site on the web and jump to conclusions about your website or business.

More informations about Disavow Link Tool , you can follow the next links :

http://googlewebmastercentral.blogspot.ro/2012/10/a-new-tool-to-disavow-links.html

Read here about WHO should use disavow links ! Seomoz article

Then direct link for you to take action is :
https://www.google.com/webmasters/tools/disavow-links-main?pli=1

If you have the time , check Matt Cutts explaining this link here :