Penguin Everflux — December 10, 2014
A Google representative said that Penguin had shifted to continuous updates, moving away from infrequent, major updates. While the exact timeline was unclear, this claim seemed to fit ongoing flux after Penguin 3.0 (including unconfirmed claims of a Penguin 3.1).
Penguin 3.0 — October 17, 2014
More than a year after the previous Penguin update (2.1), Google launched a Penguin refresh. This update appeared to be smaller than expected (<1% of US/English queries affected) and was probably data-only (not a new Penguin algorithm). The timing of the update was unclear, especially internationally, and Google claimed it was spread out over "weeks".
Penguin 2.0 (#4) — May 22, 2013
After months of speculation bordering on hype, the 4th Penguin update (dubbed "2.0" by Google) arrived with only moderate impact. The exact nature of the changes were unclear, but some evidence suggested that Penguin 2.0 was more finely targeted to the page level.
Penguin 1.1 (#2) — May 25, 2012
Google rolled out its first targeted data update after the "Penguin" algorithm update. This confirmed that Penguin data was being processed outside of the main search index, much like Panda data.
Penguin — April 24, 2012
After weeks of speculation about an "Over-optimization penalty", Google finally rolled out the "Webspam Update", which was soon after dubbed "Penguin." Penguin adjusted a number of spam factors, including keyword stuffing, and impacted an estimated 3.1% of English queries.
