If you're concerned that Google's move to mobile first indexing might negatively affect your site's visibility and search engine ranking...
Ethical SEO vs. Black Hat SEO
Ethical SEO refers to the process of optimising a website within the guidelines of the search engines (i.e. Google, Yahoo, etc). If techniques are used that are not within these guidelines, or are designed primarily to deceive the search engines are seen as unethical techniques.
To take this a step further, these techniques have been classifed with different coloured SEO hats. There are many different types of SEO ‘hats’, although most people know about the main three; the first being white hat SEO which refers to ‘ethical SEO’. Unethical or spam techniques are called ‘black hat SEO’, and when it’s a fine line between ethical/unethical this is referred to as ‘grey hat SEO’.
So why would you choose to employ black hat or unethical techniques on your website? Well, if you can get away with it and successfully deceive the search engines, you could get some great results such as high volume of traffic to your site. The flip side of this is that the results are generally short lived, and if you get caught or discovered (as you undoubtedly will) the penalties can be high, resulting in penalisation or a complete ban from the search engine altogether.