The proliferation of cyberattacks by rivals is presenting a challenge to the Biden administration as it seeks to deter intrusions on government and corporate systems. Just as it plans to begin retaliating against Russia for the large-scale hacking of American government agencies and corporations discovered late last year, the Biden administration faces a new cyberattack that raises the question of whether it will have to strike back at another major adversary: China. Taken together, the responses will start to define how President Biden fashions his new administration’s response to escalating cyberconflict and whether he can find a way to impose...