Since the olden days, black magic was used by malevolent individuals to cause harm to others. A bloke who wanted revenge or was spiteful against another could use these spells to hex that person, causing them undue harm, attract bad luck, or even death. These spells were found in books written by dark wizards who were often ostracized from magical communities and considered rogue practicioners. Since jump, governmental authorities have tried to limit the spread of black magic through the burning of books and individuals who used them, with various success. As the centuries pass however, this task becomes more difficult.
One of the problems is that the ingredients of these spells are commonplace. While certain ingredients for certain spells may be difficult for the average person to get easily, most are used in everyday life and are found in traditional items. The state can't simply confiscate and ban the usage of items or material that are necessary for the function of society.
The second problem is the rise of the internet. We have long since passed the says of book burning and private libraries, and have entered the information age where everything can be found with the click of a button. Someone could access or upload practically anything on the web, such as the Necronomicon, for little cost. Illegal downloads from wizytorrents, self help videos from MagicTube, and other sources of info exist which can educate anyone on anything.
This has the likely hood of black magic becoming commonplace without any real way to regulate it. People will just run around hexing the crap out of people fairly regularly. How can this be prevented?