Bad links or so called malicious links pointing to your site can cause serious damage to the ranking of your website. There is not much you can do if a person or a black hat SEO company does that. As the competition gets tougher out there in the net it can hit anyone.
But there is hope. Until Google finds a way of finding the darkies, you have to check the links pointing to your site(moz.com, Google Tools,…). If you find some then use the Google disvow to neutralize them.
And …. Make sure you choose a White Hat SEO company!