Google Penguin is a code name for a Google algorithm update that was first announced on April 24, 2012. The update is aimed at decreasing search engine rankings of websites that violate Google’s Webmaster Guidelines by using now declared black-hat SEO techniques involved in increasing artificially the ranking of a webpage by manipulating the number of links pointing to the page. Such tactics are commonly described as link schemes. According to Google's John Mueller, Google has announced all updates to the Penguin filter to the public.
Effect on search results
By Google’s estimates, Penguin affects approximately 3.1% of search queries in English, about 3% of queries in languages like German, Chinese, and Arabic, and an even bigger percentage of them in "highly spammed" languages. On May 25, 2012, Google unveiled another Penguin update, called Penguin 1.1. This update, according to Matt Cutts, was supposed to affect less than one-tenth of a percent of English searches. The guiding principle for the update was to penalize websites using manipulative techniques to achieve high rankings. The purpose per Google was to catch excessive spammers. Allegedly, few websites lost search rankings on Google for specific keywords during the Panda and Penguin rollouts.[according to whom?] Google specifically mentions that doorway pages, which are only built to attract search engine traffic, are against their webmaster guidelines.
Penguin 3 was released October 5, 2012 and affected 0.3% of queries. Penguin 4 (AKA Penguin 2.0) was released on May 22, 2013 and affected 2.3% of queries. Penguin 5 (AKA Penguin 2.1) was released on October 4, 2013, affected around 1% of queries, and has been the most recent of the Google Penguin algorithm updates.
Google may have released Penguin 3.0 on Saturday, Oct 18, 2014 
The difference between Penguin and previous updates
The strategic goal that Panda, Penguin, and page layout update share is to display higher quality websites at the top of Google’s search results. However, sites that were downranked as the result of these updates have different sets of characteristics. The main target of Google Penguin is spamdexing (including link bombing).
Google’s Penguin feedback form
Two days after Penguin update was released Google prepared a feedback form, designed for two categories of users: those who want to report web spam that still ranks highly after the search algorithm change, and those who think that their site got unfairly hit by the update. Google also has a reconsideration form through Google Webmaster Tools for 700,000 sites.
Confirmed Penguin Updates
- Penguin 1 on April 24, 2012 (impacting around 3.1% of queries)
- Penguin 2 on May 26, 2012 (impacting less than 0.1%)
- Penguin 3 on October 5, 2012 (impacting around 0.3% of queries)
- Penguin 4 (AKA Penguin 2.0) on May 22, 2013 (impacting 2.3% of queries)
- Penguin 5 (AKA Penguin 2.1) on October 4, 2013 (impacting around 1% of queries)
- Penguin 6 (AKA Penguin 3.0) on October 17, 2014 (more information awaited)
- Penguin Gets Official Name
- Webmaster Guidelines - Webmaster Tools Help
- Link schemes - Webmaster Tools Help
- Barry Schwartz (20 February 2013). "No, Google Hasn’t Released Unannounced Penguin Updates". Retrieved 29 April 2013.
- Another step to reward high-quality sites - Inside Search
- "Google Penguin Update 3 Released, Impacts 0.3% Of English-Language Queries". Matt Cutts. 2012-10-05. Retrieved 2013-06-16.
- "Penguin 4, With Penguin 2.0 Generation Spam-Fighting". Matt Cutts. 2013-05-22. Retrieved 2014-07-10.
- "The Penguin 2.1 Spam-Filtering Algorithm". Matt Cutts. 2013-10-04. Retrieved 2014-07-10.
- "Google Penguin 3.0 Likely Released Saturday Morning".
- Official Google Webmaster Central Blog: Page layout algorithm improvement
- "Google Updates Its Page Layout Algorithm To Go After Sites "Top Heavy" With Ads". SearchEngineLand.com. 2014-02-10. Retrieved 2014-07-10.
- "Feedback on our recent algorithm update ("Penguin")". Docs.google.com. 2012-04-24. Retrieved 2013-06-16.
- "Another step to reward high-quality sites". Official Google Blog. 2012-04-24. Retrieved 2014-05-27.
- "Google Releases Penguin Update 2". Matt Cutts. 2012-05-26. Retrieved 2014-05-27.
- "Google Penguin Update 3 Released". Matt Cutts. 2012-10-05. Retrieved 2014-05-27.
- "Penguin 4, With Penguin 2.0 Generation Spam-Fighting". Matt Cutts. 2013-05-22. Retrieved 2014-05-27.
- "Penguin 5, With The Penguin 2.1 Spam-Filtering Algorithm". Matt Cutts. 2013-10-04. Retrieved 2014-05-27.
- "Penguin 6, With The Penguin 3.0 Spam-Filtering Algorithm". Barry Schwartz. 2014-10-18. Retrieved 2014-05-27.