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.
If you've done as much as you can to remove the problematic links, and there are still some links you just can't seem to get down, that's a good time to visit our new Disavow links page.