Google new explanation on Unnatural links to your site—impacts links by Matt Cutts
If you see this message on the Manual Actions page, it means that Google has detected a pattern of unnatural, artificial, deceptive, or manipulative links pointing to your site. Google does not consider such links for ranking. Further more Google understand that these links may not be in control of webmaster and reject them,
Google said it is unlikely for you to see anything in that manual action section because "under 2% of domains" in the Google index "are manually removed for webspam," according to Google.
The parts of the site affected by each manual action. If a manual action affects more than 1,000 URLs or sections, only the first 1,000 matches will be displayed. You can have more detail in below video
We've just launched a nifty new Webmaster Tools feature that enables all verified site owners to see if a manual spam action has been applied to their site. - John Mueller
You can take measure to remove the bad backlinks
More study at Mohnesh Kohli Post on Google manual actions
