Black hat SEO

some other techniques are :
Link purchase from Link farms
Clocking

 

unethical techniques are called Black hat technique
like : clocking, doorway pages, link farms

 

fully agreed with denverice and seoshel

 

clocking, doorway pages, spamming, hidden text, link farms, keyword stuffing , meta tag repeat

 

Dodgy SE dealings is black hat. Short term and a poor business decision.

 

Blackhat SEO is anything that violates the search engine guidelines. Some of the examples are: link spamming, cloaking, keyword spamming, etc.