"Black hat" SEO are methods to try to improve rankings which are disapproved of by the search engines, typically because they consider such methods deceptive, and unrelated to providing quality content to site visitors. Search engines often penalize sites they discover using black hat methods, by reducing their rankings or eliminating their listings from the SERPs altogether. Such penalties are usually applied automatically by the search engines' algorithms, because the Internet is too large to make manual policing of websites feasible.

Spamdexing is the promotion of irrelevant, chiefly commercial, pages through deceptive techniques and the abuse of the search algorithms. Over time a widespread consensus has developed in the industry as to what are and are not acceptable means of boosting one's search engine placement and resultant traffic.

Spamdexing often gets confused with white hat search engine optimization techniques, which do not involve deceit. Spamming involves getting websites more exposure than they deserve for their keywords, leading to unsatisfactory search results. Optimization involves getting websites the rank they deserve on the most targeted keywords, leading to satisfactory search experiences.

When discovered, search engines may take action against those found to be using unethical SEO methods. In February 2006, Google removed both BMW Germany and Ricoh Germany for use of these practices.

Cloaking is the practice of serving one version of a page to search engine spiders/bots and another version to human visitors.