Google updated their Penguin algorithm, specifically they called this a “refresh”. Google penguin refresh algorithm that focus to looks at poor back link profile. Refers to Google’s Pierre Far update on Google+, it’s affecting fewer than 1% of queries in US English search results. He also said It’s a slow worldwide rollout, so you may notice it settling down over the next few weeks.
According to Search Engine Land, a refresh in Google’s terminology around algorithms means they just re-ran the algorithm to release sites that fixed their issues and demote sites that had issues they didn’t pick up on. So, may previously sites that got the ranking drop would go up in the search results because they are no longer negatively impacted by the algorithm. otherwise, may the other sites will see a ranking drop because they were just picked up as sites that should be impacted by the Penguin algorithm.
This issue certainly will make a little worried the SEO and webmaster. Because maybe they will see a change in the ranking of search results extremely than usual. But don’t get enough information to explain why it happened.