Invisible Text - Search engines can see you, and don't like you for it!

Simply put, do NOT use invisible text to keyword stuff content in the text on your page! Using 'invisible' text is the practice of making the colour of the text on the page the same as the background colour. This ia an 'old' black-hat SEO technique. As an example... white letters on a white background qualify as hidden text. The reason that many search engines have banned this kind of text is because it is VERY hard to detect it. This is usually a result of the vast number of colour combinations that have to be recognized when an engine 'spiders' the page.

As an example: You have a web page that uses a background colour of #FFFFFF (white). You then place text on the page and slightly alter the colour to make the colour of the text #FFFFF0 (off-white), which would now be ALMOST totally invisible.

Many, but not all, of the major search engines now have a policy against this type of technique, and have set up their indexing programs to hunt it down and blacklist the site because of it. When spotted by a bot, the penalty can range anywhere from ignoring the text, to refusing to index the page at all, or even worse. This type of practice is regarded as a black-hat SEO SPAM technique by most of the search engines and it highly recommended to avoid including it on your page.

Of course you may come across a well ranked page here and there that is still using hidden text. This should be taken more as an indication that the page has not been re-indexed since the tactic was made 'illegal', than an indication that the search engine allows this practice. Basically, most SEO's have come to regard hidden text as too risky, and have moved on from it.