The international nature of ransomware crime is also an impediment to bringing it under control. The Justice Department and FBI are working with allies and partners overseas to investigate criminal rings, disrupt their operations and online infrastructure, and prosecute hackers, officials said. In January, the department joined Canada, France, Germany, the Netherlands and Britain in dismantling the botnet known as Emotet, which had infected hundreds of thousands of computers in the United States and caused millions of dollars in damage worldwide. The botnet, an army of hijacked computers, could also be used to spread ransomware.