Google being the world’s biggest search engine, needs certain kinds of ranking system, that might be able to rank the websites that are the most frequently searched. Thus, to measure the importance of websites, a kind of page ranking is done frequently.
And every time Google updates its search algorithms i.e. the tool which finds out the page ranks, there have been instance when a page had been negatively penalized due to various black-hat SEO techniques that might be utilized by certain websites to spam the users as well as to higher their page views.
Some of the noteworthy cases have been seen in the year 2009 as well as in 2013 (on the release of Google’s Penguin Algorithm) when the website Overstock.com was penalized for having poor SEO techniques.