These links are purchased by some kids from hacker websites with webshell, which is very cheap. Just like an article I submitted to admin5 last year, it mentioned a sentence: "Baidu responds quickly but does SEO slowly." If you want to do something, use a technology to do it; if you use this technology to do another thing, it would be more profitable. Of course, that article did not have this sentence. It was just my summary. Since that article also mentioned the thought about black hat SEO, so I pulled it out to talk about it. This article is just the beginning of black hat SEO, so there is no much content on SEO. The following several articles will only write about technology, not these theories.