You may have assumed that all your purchased links that have passed PageRank are clean. However, you need to re-check those links to confirm if they are indeed squeaky clean since Google has now started taking manual action against Links Sellers.
Matt Cutts from Google has confirmed that the company has taken action against thousands of link sellers that had passed PageRank. However, details have not been provided on the names of networks that had been penalized by Google or in fact whether they were in-house link networks.
Based on Matt’s tweet, it does seem that rather than using an algorithm that automatically targeted such links, Google seems to have initially focused its attention on taking manual action against specific link sellers. This action comes in the wake of Matt’s recent webmaster video “What to Expect” in which he explained in detail about link devaluing.
So, it may be wise to quickly get back to your links and scrutinize them thoroughly if you want to avoid Google’s manual crackdown.