Black hat…

Summary:

Blackhat methods are considered "high risk". They can provide you with a quick fix, but they can also get your site banned from the serps

White hat guidelines
Almost every search engine has specific guidelines for sites to be included in its index. They preserve the right to remove your site's listing from the index if you break their rules. From Google's guidelines (and more or less the same goes for other search engines) these are the common things to avoid:

• hidden text or hidden links.
• cloaking or sneaky redirects.
• sending automated queries to Google.
• loading pages with irrelevant words.
• creating many pages or (sub)domains with mostly duplicate content.
• "doorway" pages or affiliate programs created just for search engines, with little or no original content.

Not against the law
Of course there is no law that says it's illegal to use these methods — some of them are just considered to be less ethical, but even that is open to debate… Fact is that these tricks are against the search engines' TOS. So the problem remains that if you're nicked, your site can be dropped from the results pages. Of course there are methods that are against the law, like unauthorised copying of content, libel, and fraud.

Black hats on cowboys
Given the proclaimed "evil" nature of these methods, the people using them anyway are said to practise Black Hat SEO. The term has its origins in old cowboy films where the hero always wears a white hat, and the villains black hats. Just that we "simple folk" could easily tell the good guys from the bad guys - heh.

BH takes effort too
Even though these methods have the power to give your site an artificial boost – either in traffic or in SE ranking – there's still a lot of hard work involved. There are keywords to be chosen, pages to be made and optimised and backlinks to be scored. Whereas an amateur blackhatter will happily do all this by hand, a real pro will soon resort to automation. There are several pieces of software available to make the burden of blackhat more bearable. Programs like Articlebot, Kloakit and Shadowmaker are famous examples.