When you receive gear, you have a random chance to receive a cursed piece of gear. It will be red and labeled cursed. It will be a lower level until purified. Instead of boosting random stats, it will drop them. It will tell you what you need to do to purify it. I've received 2 cursed gear so far and both required me to kill 3 disciples. Once completed, it will purify immediately and will raise it's level and replace negative stats will ones that will boost. Make sure you have it equiped in order to purify it. Has to be done on gold difficulty.