Invisible text
 

Although this may be an obsolete bad SEO strategy, this is absolutely worth mentioning, in order to prevent anyone to make such a mistake. Some web sites hidden in the words on the page, in an attempt to (for example, you can use cascading style sheets - CSS hide or black in the black background text defined as page elements), artificially increase the correlation of key words. For many years, greatly improve the search engine's spam filter, you can't get any benefits, the application of this technology, in the worst case, you will be banned from the search engines.

If search engines ban the websites that contain invisible text or hidden text than why website owners do this.

As we have in the search engines know whether the web content related (relevant content)? "File will use articles, search engine relationship between the understanding of web anchor text (an anchor text)to be judged, and the content of the pages there will be keyword stuffed (keyword stuffing), and for the human link (link spam) algorithms to detect.