Identifying bad links pointing at your site gets you half way to solving a possible problem. There is little you can do until you know what is going on. Truth be told, not all bad links are a product of a negative SEO campaign. Sometimes website owners / SEOs themselves can create troubles for their sites by not being careful enough and too greedy for easy links.
How do you define a bad link nowadays? At the very least, a bad link is the one that:
•overdoes your anchor text a bit too much (not seen on the individual links level but en masse);
•comes from a site either de-indexed by Google or on its way to de-indexing;
•an obviously paid link;
•a hidden link.
http://www.searchenginejournal.com/how- ... der/56921/