It's one still employed today. That of burning domains, redirection and volume buying of low quality links. This technique makes use of the honeymoon period Google applies to new domains before PageRank and other metrics have been applied. Search for pay day loans, click almost any link and I'll bet the domain you end up at isn't the same one you originally clicked.
The worst black hat SEO tactic I've ever come across will always be the good ol' link spammer. Link spamming is incredibly obnoxious and tends to reign throughout sites and blogs ALL over the web.
Link spamming is one of the most offensive black hat SEO techniques. This tactic involves spamming comments, forums and other web outlets with links. You may have come across a comment or two that was riddled with links and added absolutely nothing to the discussion. This is the kind of thing you want to refrain from practicing. Because of abuse, most of these links now come with the “nofollow” attribute. This means that Google will not count this link toward your website. In addition, doing this will surely earn you a bad reputation with bloggers and readers.
-Noah
Bad backlinking is mostly used black hat SEO tactic and still in use.
* putting bad review or bad comments about any company will lead to decrease in popularity.
* As google considers backlinks for ranking, it will even ruin decrease the search engine ranking.
* bad backlinks results very less traffic to website and zero conversion rates. To make them good backlinks its will take much time.
Recently fred update was made to find out the bulk domain links.
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