Google has released Panda Update to combat the websites with duplicate content and low quality links. The update has really worked and many web sites that have plagiarized content have been disappeared form the top SERP's (Search engine results pages).
Till date more than 20 Google Panda Updates were released and 14.4% of total sites present on the internet got affected by the Panda Update. These Google updates has led numerous companies with main operations as SEO to promote the importance of maintaining good content and earn money by developing several plagiarism tools that detects copied content in the web pages.
At present, there are more than 3,000 duplicate content checking tools over internet and over 287 blog posts were updated by Seomoz with content related to the Google panda update. The changes made in Google search algorithm has led many spam fighting individuals like Matt Cutts, Rand Fishkin, Will Crithclow and Aaron wall etc to promote the necessity of unique and high quality content to get good page rank.