Google has confirmed that it began another Google Panda refresh this weekend. Google Panda was first released in February 2011 and involved a change to Google’s search ranking algorithm that aimed to lower the rank of “low quality sites” and return higher-quality sites with rich content near the top of the search results.

The original Panda update had a huge impact on the SEO industry and online publishing as a whole, but you probably haven’t noticed any impact from Panda 4.2 so far. This is because it is rolling our very slowly. Google has confirmed that only about 2-3% of English language queries have been affected so far.

Which sites are likely to be affected?
The slow rollout is not how previous Panda updates were done, where typically sites saw dramatic increases or declines in traffic overnight. But, if you were penalised by Panda previously and made the right changes to combat a drop in traffic you might see further improvement to your search rankings gradually over time with Panda 4.2.

Source: http://searchengineland.com/google-panda-4-2-is-here-slowly-rolling-out-after-waiting-almost-10-months-225850