In order to talk about unfair competition in search engine optimization, we must first define what this practice refers to:
We will call unfair competition or black hat to the malicious use of keywords, links or features that refer to a brand of the competition of our site for our own benefit or negative actions such as spam content, which we put or provoke others.
Nowadays we can all be victims of this practice, that is why to avoid it there are tools that help us to know if our site is being plagiarized, attacked or if it is vulnerable to this type of unfair competition.
On the other hand, there are also ways to prevent our competitors from misusing our ideas, articles, images, words and brands, so you should know or at least get advice from a good computer lawyer.