What are the key aspects of Penguin update
 

Penguin is the code name for Google algorithm. Its main target is to decrease the ranking of that website that are violating the Google Webmaster guidelines. These guidelines are violated by using black hat techniques like cloaking and stuffing.

Google Penguin included violating the google webmaster guidlines that stuffing meta tags with keywords and also acquiring high volumes of anchor text links from weak domains.

Penguin update mainly targets sites that has low quality backlinks, link farms or link wheels.

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Penguin update specifically targets those websites that are using link schemes in order to manipulate the rankings and the worst will be penalized as well as de-index in their database.

penguin update
 

penguin update hit those website who have irrelevant and low quality backlinks. so if aspects this update by analyse your website backlinks and discard low quality backlinks.

Both are for reduce the spamming and make web more informative not with full of spamming, Basically panda check content of webpage and penguin check links quality, so if you want to protect your site from such update you must focus on building quality link with unique content.