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We dropped significantly (from page 1 for 4 keywords...to ranking over 75 for all) after the Penguin update. I understand trustworthy content and links (along with site structure) are the big reasons for staying strong through the update...and those sites that did these things wrong were penalized. In efforts to gain Google's  trust again, we are checking into our site structure and making sure to produce fresh and relevant content on our site and social media channels on a weekly basis. But how do we remove links that were built by our SEO company, those of which could be untrustworthy/irrelevant sites with low site rankings? Try to email the webmaster of that site (using data from Open Site Explorer)?