Illegal SEO techniques are those that violate search engine guidelines, such as using too many keywords in your website, hiding text in your website, and exchanging links. These techniques may allow your website to be recognized as spam by search engines, which can lead to downgrading of your website. For example, if you use too many keywords, stack keywords in your pages or use some irrelevant keywords, search engines will think that your website is trying to cheat search engines and will downgrade your website. Therefore, make sure that your website follows the search engine guidelines and uses co...