Ji and more than 2,600 Chinese nationals claimed to work for two U.S.-based companies that do not exist, according to court records. That allowed them to remain in the country without authorities detecting them, and exposed a hole in the nation’s immigration laws. The alleged fraud scheme raises questions about how well the government monitors and regulates the popular student work program and whether any of the other students might be spying for China. Federal officials said no changes to the program were planned.