Penguin 4, With Penguin 2.0 Generation Spam-Fighting, Is Now Live
Matt said this is being rolled out “within the next few hours.”
Penguin 1 on April 24, 2012 (impacting ~3.1% of queries)
Penguin 2 on May 26, 2012 (impacting less than 0.1%)
Penguin 3 on October 5, 2012 (impacting ~0.3% of queries)
Penguin 4 on May 22, 2013 (impacting 2.3% of queries)