Most search engines consider hidden text to be spam -- but there are several kinds of hidden text, and Web designers use some kinds of hidden text for legitimate reasons that have nothing to do with fooling a search engine into giving the site a high rating. How do you know if you're courting a permanent ban? Burhan Khan explains the different types of hidden text, and how they are treated by the search engines.
We often talk about "hidden text," but in reality what is hidden text? Hidden text is also known as "invisible text" or "fake text." Hidden text is often used for spamming the search engines. But many smart search engines, such as Google can detect the use of hidden text. To give a simple definition, hidden text is text on a Web page which is visible to search engine spiders but not visible to human visitors.
You should not use hidden text to get high ranking in search engines. By hiding keywords in hidden text, you may be able to trick the search engines for a limited amount of time. Anything that hides text from a browser, but is still in the body of the document, will be indexed by the search engine spiders. But the use of hidden text can cause search engines to permanently ban your website.
Some years ago, search engine optimization consisted of putting a group of phrases together with as many repetitions as possible to make up a keyword tag and, if necessary, putting the same text in a hidden form at the bottom of the pages. This was a very easy method of getting visitors, but some people overused this approach, to the point of abusing the system. Because of this abuse, search engines took action to stop this kind of search spam. The effect of this is that the actual keyword tag is virtually useless now, and hidden text is likely to get your site banned from the search engines instead of helping it!
Search Optimization 
