Negative SEO is a cruel technique whereby one does something underhanded to sink a competitor's rankings. One method of negative seo, for instance, is to purchase links on link farms that point to a competitor's website. If that competitor does not monitor its backlinks (and put up a new disavowal list) it will soon find itself penalized by Google. Another method is hacking the competitor's website and modifying its content. Still another is scraping content from a target site and spreading it around on unsavory websites. For karma's sake, we do not recommend any of these techniques.