In fact, I reported yesterday at Search Engine Land that No, Google Hasn’t Released Unannounced Penguin Updates. Why did I have to report that? Couple reasons:
(1) There was some speculation based on a video hangout with John Mueller that Penguin refreshed regularly. It does not, it never did, and the truth is, it refreshes very rarely.
(2) It has been almost five months since an official Penguin update and I wanted to make sure we didn't miss any updates.
Google has told us that Penguin is rarely refreshed, unlike Panda and we didn't miss any Penguin refreshes since.
What was John talking about? He was talking about normal link analysis is refreshed and rerun continuously.
I posted this on my Google+ page and then someone brought up the Zebra update. There is no such thing, stop asking me about Zebras. There was not a Zebra update.
Forum discussion at Google+.