This isn't exactly a cyber security topic but protecting your website is and this could be something that is happening to you. First off, what is negative SEO? In April 2012 Google launched an algorithm called penguin. From that moment foward, negative SEO was born. You could now build spam links to your competitors or to knock out undesirable search results for managing your brands reputation. It wasn't just this algorithm Google launched that made this possible, but this was the beginning of several anti-spam black hat SEO algorithms released. You can see a full history at moz right here.
In October 2012, Google who had all along said in no uncertain terms you can't be hurt by negative SEO, released a disavow tool. This now made it possible to get rid of unwanted links that point to your website. You would think negative SEO is dead, right?