SEO is a way of generating organic traffic from search engines. In the world of SEO, there are many techniques that companies can implement in order to boost their SERPs. Different companies are using different SEO tactics, and those techniques keep changing as Google changing their algorithms. There are safe ways of doing SEO and there are risky ways. In the world of SEO, we usually call safe ways of doing SEO: “White Hat”, and we call risky ways: “Black Hat”. Of course, there is “Grey Hat”, but I am not going to explain that in this article.
Black Hat SEO techniques are basically used to boost SERPs in a very short amount of time. They are usually practices that Google disapproves or dislike. If a website were caught doing Black Hat SEO techniques, it will be penalized, and sometime be sandboxed or de-indexed. In general, Black Hat SEO techniques are used in order to beat Google algorithms, and they are only focus on Search engine but not for providing good users experience .

Following is the List of Black Hat SEO Techniques You Should Avoid:

1. Hidden Text/ Links
This technique is basically trying to add content to the page, but it doesn’t want visitors to see it. This technique usually is used on flash websites or very graphic sites.
For Examples:
-Write texts in a very small font size and use font color same as the background color
2. Keyword Stuffing
Keyword Stuffing is a technique of trying to use a certain keyword phrase repeatedly throughout the page, and trying to fool search engines that the website is relevant to the keyword phrase.
For Example:
- SEO is good, SEO is best, SEO is the key…. (goes on and on, in hoping of ranking the keyword “SEO”)
3. Rich Snippet Markup
Rich snippet is a very good way of  increasing the percentage of clicks from search engines. There are many types of rich snippets. Star rating is the most popular one and it is often used for product rating, but it is often been abused as abused as well.
For Example:
- John created the fake 5 star rating rich snippet on a product, but he controls how his product should be rated, but not users.
4. Doorway Pages
Doorway pages technique is used to spam index of search engines; we usually call it “Spamdexing”. Basically, it is when the pages is different from the search results description. This usually can be achieved by using meta tag and Javascript to redirect visitors to a completely different site.
For Example:
-  A website has keyword phrase and description, but the site is showing completely different from them.
5. Article Spinning
This one is very popular in the recent years. Basically, article spinning is you find an article online, and then using software to spin the articles, and then submit them to web 2.0 websites. Very often, those articles are created for search engines, not for human, because 90% of time they are not humanly readable.
6. Cloaking
Cloaking is similar to doorway pages technique. Basically, cloaking is making one version of content to search engine spiders and another version of content to actually users.
For Example:
- When John searched for computer software on Google, and then after he clicked on one of the search result link. Instead of a computer related website, he landed on an accounting website.
7.  Buying Links
Link exchanging or links buying technique has been a popular technique of increasing the SERPs. It is basically a way of cheating on SEO.
For Example:
- John paid $200 to Smith for placing a link on his high pr website.
8.  Social Media Spamming
Social media spamming is quite common these day. Don’t get me wrong, promoting sites via social media is good, but don’t overdo it. Because it is annoy to your followers or fans.
For Example:
- John setups an automation program that is allowing his same promotional message to tweet repeatedly for every 2 minutes.
9. Link Farms
Link farms technique is the reciprocal linking tactic that is basically describe a group of similar websites linking to each other. It is like links exchange, so that everyone is gaining link juice from each other.
For Example
- There are three very related websites:  A, B, and C. Website A is linking to websites B and C;  website B is linking to A and C; and website C is linking to A and B
10. Spam Comments
Spam comments technique is using tools to  spam comment section of posts and add backlinks. Usually, instead of manually commenting, people will use software to speed up the process. First, it will scrape the search engine for blogs that allow comments, and then they will use spun comments to auto commenting those posts using different IPs. It is one of the top black hat technique that allow people gaining massive backlinks overnight (mostly nofollow links).

Summary

In fact, there are still a lot of black hat techniques that I have not mentioned here. The above ten, I think,  used to be the most popular black hat techniques, and some of them still are.  If you are using any of techniques above, you should stop doing them. Sooner or later, Google algorithms will catch up, and it will be too late for you.  As always, please leave a comment if you have any comment or suggestion.