Aiming to give webmasters a tool to disassociate their sites from unwanted links, Google on Tuesday introduced a feature for webmasters called "Disavow Links."

Using the new feature, announced at the Pubcon conference in Las Vegas, anyone who controls a website can tell Google which links to their sites they'd like to ignore. In the video below, Matt Cutts, the head of webspam at Google, explains that the site is for reformed spammers who might have been doing comment-spam or blog-spam before, but now have cleaned up their act and want to get back into Google's good graces. Google often notifies webmasters when such links exist and is working on ways to include some URLs to illustrate the types of links it finds "unnatural," Cutts says.

Cutts suggest first trying to get the links removed from the web. If that approach fails, he advocates using Disavow Links to notify Google. Cutts stresses that mom-and-pop operations that haven't engaged in SEO gaming are unlikely to have to use the feature.

For others, the idea is that if you have spammy links you can ask Google to disavow it or even disavow an entire domain. Cutts says Google treats such requests as a "very strong suggestion," but not something Google has to abide by. If Google acts on your suggestion, then it will remove the link within a few weeks.

http://mashable.com/2012/10/16/google-disavow-links-spam/

This service can be accessed via Google webmaster tools, or here https://www.google.com/webmasters/tools/disavow-links-main?pli=1