In the introduction to its technology, Google states that it uses a unique combination of advanced hardware and software and that at the heart of the software part is the PageRank system.
This particular tool is very powerful, as many website owners have discovered, for it allows an unbiased ranking of web pages in the Google search engine result pages. PageRank picks up the number of links that point to a particular website as an indicator of its search engine standing. But it gives priority to websites that have been linked to by sites that in their own right enjoy high PageRank.
Due to such stringent measures undertaken by the giant search engine, it is important that website developers and website designers construct web pages that do not over-do SEO techniques like link building, keyword optimization, anchor text linking, etc.
Hidden texts, link building in a domain that is considered unsafe (pornographic sites) and fooling the search engine using a version that is different than the one displayed for the visitor, too call for a penalty to be placed on a website.