The company posted the news on Twitter, saying this update will affect about one percent of search results.
New data refresh of Panda starts rolling out tonight. ~1% of search results change enough to notice. More context: goo.gl/huekf — A Googler (@google) July 24, 2012The previous update (3.8) occurred a month ago — on June 25th.
Panda rolled out initially in February 2011 and was designed to remove low-quality/thin content from Google’s search results.