Black hat seo techniques are
1.Paid Links
2.Spam Comments
3.Duplicate Content
4.Article Spinning
5.Cloaking

In search engine optimization (SEO) terminology, black hat SEO refers to the use of aggressive SEO strategies, techniques and tactics that focus only on search engines and not a human audience, and usually does not obey search engines guidelines.

8 Risky Black Hat SEO Techniques Used Today

1 Paid Links
2 Spam Comments
3 Duplicate Content
4 Article Spinning
5 Cloaking
6 Doorway Pages
7 Keyword Stuffing
8 Invisible Text