Penguin 4 rolled out today affecting 2.3% of all English-US queries. What makes Penguin 4 different than its predecessors is that Google updated the webspam algorithm to better stop spam.
From Matt Cutts: “The change has also finished rolling out for other languages world-wide. The scope of Penguin varies by language, e.g. languages with more webspam will see more impact.”
This update is expected to have the largest impact since the initial Penguin launch last April.
Google launched Penguin in 2012 to help catch websites they deemed to be spamming search results, specifically through unnatural linkbuilding practices such as purchasing links and spam directories.
It will be interesting to see which type of queries will see the largest fluctuations in the upcoming weeks.