Google Penguin
What is Negative SEO?

Negative SEO is the attack on competitors sites by employing black hat SEO tactics, generally by use of poor quality backlinks that lead to the rival competitor's page or pages to cause penalties on the rivals page ranking. Though having a great SERP relies more on other analytics of the webpage, not just quality backlinks, poor quality backlinks could still radically decrease a competitors ranking.

Before Google's penguin came along it was much harder for rivals to implement the search engines penalties and knock competitors out of their ranking, as the use of poor quality backlinks were really the only black hat tactic that could be used against a competitors webpage, unless the rival could hack as well. However Google has gone through a lot of changes over the past 8 months, changes that left Google and those of us who use white hat SEO bent over for those black hat rivals.

Google of course is in the state of denial, believing that some of the new calculations (such as the block this site data received from the Google chrome extension) that penguin implements will help people find what they are searching for better, when in reality penguin has left the door wide open for rivals to destroy a competitors ranking while they further employ spamming optimization methods and still have a great SERP.