Which black hat SEO techniques still work today?

Hiding Keywords:

Keyword Stuffing , which would be excessive use of keywords (example here already cited , the keywords are well below the page and will generally go unnoticed by the visitor), however this can be done so that the visitor does not can see it.

As? Using a background without image and with the same color of the source.

This can already be detected by search engines.

You can also overlay two layers of CSS and make keyword stuffing in the overlapped layer.

Another way is to use a very small font, imperceptible to the visitor.

Hiding Links:

In the same way that you hide the keywords can be done also for links, the effect is the same.

Keywords not reported in the subject :

Using keywords of little relevance to the subject or sometimes none the developers aim to generate more traffic, reporting keywords that were being searched for.

In the past keyword sex was reported in the KEYWORDS tag for this purpose, but over time it got so crowded that today it will not have any effect.

Page swapping :

A little used technique where the page is changed, shortly after the search engine, for a page not optimized.

The difficulty in this technique is in knowing when the search engine will do the next indexation because this can be done with a very large frequency, which makes this technique little effective.

Show different pages for different types of visitors:

Intend and show different pages for human and search engines.

If the site was built with invisible technology, a searchable indexable version may be presented, different from what the user sees.

In another situation the search engines have different algorithms, and so a different and optimized version of the page can be shown for each search engine.

This is done through Cloaking and Redirects.

Redirects :

It is the automatic loading of a page without human interference.

This is done for the user to go through the first page that is optimized for the next page without his noticing.

This can be done using REFRESH tag, however the search engines are already aware of this and can be considered blackhat.

Cloaking :

This is a more sophisticated method.

When a browser or a search engine visits the site, a request with an identifying information such as browser version or searchbot is sent, so a different response is sent to that request.

The pages made for the engines are simple, easy to understand and with a high density of keywords.

The pages for humans are graphically complex, attractive, with navigation structures and fewer texts.

The Cloaking is a very controversial topic that always generates discussion and can best be detailed hereafter.