The following black hat SEO techniques should always be avoided. Why should you avoid these techniques? Well because they can get you banned from all the major search engines, and because they are also very easy to detect (thus increasing chances of ban-age!) … (see them after the jump)

•  Keyword Stuffing - don’t put the same keyword again and again and again…and again. It is very easy for search engines to spot automatically, and even easier for an employee of theirs to spot
• Invisible text - again very easy to spot by search engines (how hard is it to see if the background is #FFFFFF and the text colour is also #FFFFFF (or even something like #FDFDFD…). Don’t do it.
• Doorway or fake pages – sometimes these are harder to automatically detect, but you will still get caught.

I am not in any way just discouraging all of black hat seo – some can work (for a while, at least…) and if you are lucky you may not get banned or removed from Google/Yahoo/MSN/other search engines. But just don’t be stupid if you are going to do black hat seo.