Negative SEO has been a concern for many webmasters as of late. This is because if too many bad links are pointed at a website it can potentially hurt your search engine rankings. Google of course recently came out with the disavow links tool to address this, however, bad links are still being built in some cases. For certain websites this can turn into a vicious cycle of constantly disavowing bad links which competitors are pointing at a website. In the video below, Matt Cutts from Google addresses negative SEO.