Most people doesn’t know about black hat SEO techniques. Black hat SEO is also know as Spamdexing. Following are considering as Black Hat -Keyword stuffing. (keyword stuffing include excessive use of keywords to increase SEO. ) -Hidden text and invisible text. -Link farms. Search engines takes their maximum effect to remove sites from their index, who practice black-hat methods as these methods will ; - Degrade the relevance of the search - Degrade user experience. So webmaster be careful when doing your SEO. Think long run. Do not use Black-hat methods. Do not handover your campaign to SEO firms who practice black-hat methods.