What is a major purpose of Google Penguin latest update?

1 The Penguin 2.0 and 2.1 updates are about readability metrics of content on backlinks.  So the less rare words on the pages linking to you the less Google is likely to deem the content as being authentically expert on whatever content is discussing.  This was proved with empirical evidence to a 98% statistical confidence using probabilistic methods.  Unlike correlation studies, MathSight used ANOVA to filter out coincidences to identify factors that have a causal relationship to site pages that won and lost traffic as a result of Penguin.  You can read the coverage on Search Engine Watch here: http://searchenginewatch.com/article/2323727/Dissecting-Google-Penguin-2.1-What-Factors-Mattered-Study

To penalize paid links pointing to subpages, not just the homepage.

Google Penguin is a part of Long pending Google efforts to Fight web  spam - Now web spam indicators can be found withing your own site  as well as from the sites you are linking from - earlier updates such as panda penalized  sites with shallow content or in other words written only for catering  to some keywords sets but providing no value to the users - penguin on  the Other hand aims at Fighting Link spam - when  you are getting  unnatural links such as from paid sources, link exchanges programs or  too muck optimization through exact anchor Text, just to have some  Influence on the ranking. Earlier spam updates were more or less  targeting websites as a whole but Penguin is much deeper and evaluates  each page as unique identity Thus Penguin updates is: Penalizing for Getting Unnatural Links for Keywords Getting Paid Links Getting links for suspicious sites Getting links from Unrelated and shallow sites Getting links with exact anchor Texts