Cloaking:
This method is used to deliver different pages for visitors and search engines. Webmasters configured their servers to recognize IP addresses of SE spiders and deliver them content rich, optimized pages, while showing absolutely different pages for human visitors. Cloaking may also redirect visitors to a home page. This technique is treated as spam and is not recommended to use.
* Link Farms
Many companies use this method. It's sole purpose to gain link popularity. A link farm is usually one page that consists of 50 to 100 or more links to websites that have nothing in common with the content of your site. Such pages have no benefit to users as they give links to sites that aren't interesting to them. Link farms are being penalized by search engines.