Officially now known as the Google Penguin Update, and the updates still haven't stopped. 2.0 was released on May 22nd and is said to be a deeper algorithm update with increased focus on flushing out sites that have benefited from link spam.
Previously, Google released Panda in 2011, but how does Panda differ from Penguin? Where Penguin's aim is to penalize the SEO "mistakes" of websites, Panda is an algorithm aimed at downgrading websites with poor user experiences.
By Google’s estimates, Penguin affects approximately 3.1% of search queries in English, about 3% of queries in languages like German, Chinese, and Arabic, and an even bigger percentage of them in "highly spammed" languages.
The purpose per Google was to catch excessive spammers, but it seems some legitimate sites and SEOs have been caught with this latest algorithm change. Few websites lost search rankings on Google for specific keywords during the Panda and Penguin rollouts. It appears anchor text was to blame in these cases, as the links pointing to these sites concentrated on only one or a few keywords while the content of the websites was satisfactory. As the update focused on the quality of backlinks, so the result varied for different websites. Google specifically mentions that doorway pages, which are only built to attract search engine traffic, are against their webmaster guidelines. Regardless, many people still use this technique.
The point is to keep to Google's Webmaster guidelines to avoid being penalized, but if you were hit by the Penguin update, here is a few ways to get back on track: