Even if you are new to SEO, you have already heard the term Black Hat. Believe it or not, the spammy techniques that all professional SEOs do not use and search engines hate, actually evolved along with the White Hat and also lead to constant improvements in the search engine's algorithms.
You don't believe me? Take a look at the evolution of the Black Hat SEO.
***** I believe this because I lived through much of it AND because things that were white hat yesterday such as driving links to your site from stuff you create for others now defined as "black hat" was "white hat" prior to Penguin/Panda. Google's constantly shifting line in the sand is why this chart makes all hats grey. Marty
Via Guglielmo Cornelli, John van den Brink