If your site was penalized by Google for unnatural links than this is the tool you need to use. This is a full tutorial on how to use the unnatural link detection widget.
It is also important to view how to classify the brand vs commercial anchor text before running the Automatic Classification. This is an important signal that is used in our algorithm and may influence your results. A good anchor text classification ensures a correct unnatural links classification.
Other useful articles:
http://support.cognitiveseo.com/knowledgebase/unnatural-links-are-dead-a-case-study/
http://support.cognitiveseo.com/knowledgebase/unnatural-links-the-no-bs-guide/
http://support.cognitiveseo.com/knowledgebase/unnatural-links-detection-how-to-guide-case-study/
http://cognitiveseo.com/blog/3068/automatic-unnatural-link-detection/
http://cognitiveseo.com/blog/3411/unntural-links-penguin-recovery-using-the-google-disavow-tool/
http://cognitiveseo.com/blog/3524/the-fastest-most-accurate-unnatural-link-detection-case-study/