In October Google announced the introduction of its disavow tool to finally address the issue of bad links pointing to a website. It’s a contentious issue to start with because as we’ve said before, building unnatural links (like paying for them for example) to help raise rankings has always been wrong.
Far better to get those links naturally because you’ve got great content and that’s what Penguin and Panda have been mostly about, not rewarding bad links.
However, you can’t control who links to your website and you can be an unfortunate victim of a malware attack such as the well publicised “pharma hack” earlier this year. This can result in a large number of undesirable links pointing to your website and you may not even be aware of it until Google’s webmaster tools leaves you a nice message.
You do have to demonstrate that you’ve tried to remove the links yourself and actually getting links to be disavowed is entirely at Google’s discretion, so the more work you can do to ensure it (a) doesn’t happen and (b) that you’re working hard to stop it happening, the better.
To disavow links, you have to upload a text file, with one URL per line of links that you want Google to ignore. These are the links pointing to your website that you’re telling Google that you don’t trust. To do this you need to login into webmaster tools and select the website that is in question, and if you’ve a spare 10 minutes Matt Cutts from Google tells you all about it: http://youtu.be/393nmCYFRtA
Google says: A typical use case for this tool is if you’ve done link building that violates our quality guidelines. Google has sent you a warning about unnatural links, and despite your best efforts, there are some links that you still can’t get taken down.
Here is the link to get to the right page in Webmaster tools: https://www.google.com/webmasters/tools/disavow-links-main
You can read the full detail on Google’s blog: