Search engines consider certain optimization techniques to be spam, or Black Hat. If search engines believe your site is using these techniques, they can ban it!

If you follow the guidelines published by search engines, then you are using White Hat Optimization techniques. This is the best approach to follow, because let's face it, if you follow the guidelines, the search engines will "like" your site and it will receive the ranking it deserves!

Some of the most common Black Hat SEO techniques are listed here. Unfortunately, web designers can incorporate some of these spam techniques without realizing the site could be penalized.

1. Hiding Links on your pages: This technique puts links in very small images, some as small as 1 x 1 pixels. The visitor never sees them but search engines can.
2. Repetition of keywords on your pages: It is recommended not to repeat keywords excessively in your body text or tags. This technique is used to try to add relevancy for that particular keyword/phrase.
3. Text that is not visible to your visitor: When text is hidden off page or is the same color as the page background, search engines consider it spam. You could easily get caught without even knowing it! For example; let's say your page background is white and you have a dark green color block with white text on it. This is very innocent, but search engines could flag this as spam, because the white text is the same color as the white background, even though it is on a green color block. The work around would be to change the white text to a light grey or light green, any color that is different than the white background.
4. Doorway or Gateway Pages: These are pages that have been designed to rank high on search engines. They are then set to redirect visitors to the actual website.
5. Link Exchange Free For All (FFA): There are sites that let anyone add banners or links, even if they are not relevant to the site content. Most search engines like to see "relevant links".
6. Cloaking Technique: This technique hides code from the visitor while offering search engine spiders customized content.

 The best approach to avoid Black Hat SEO techniques is to simply build sites for your visitors. Your goal should be to make your site user friendly and incorporate relevant information.

All search engines publish their own guidelines. The best approach to avoid being penalized is to review these guidelines and follow them.