Ransomware -- a type of malicious software that restricts access to a computer system until a ransom is paid -- is not a good look for cryptocurrencies. Proponents of these digital coins would rather point to celebrity investors such as Tesla founder Elon Musk, Dallas Mavericks owner Mark Cuban, star football quarterback Tom Brady, or actress Maisie Williams (Arya in Game of Thrones). But recent ransomware attacks, and cryptocurrencies' central role in enabling them, are a public relations disaster.