Another senior official declared that “the Cold War enforced norms, and the Soviets and the United States didn’t go outside a set of boundaries.” But, he argued, “China is going outside those boundaries now.”

Among those who view these hostilities as the cold war redux, some are proposing a more strident response. Earlier this year, the United States military announced the formation of 13 units dedicated to offensive cyberstrikes and endorsed pre-emptive cyberattacks. And late last month, Jon M. Huntsman Jr., the former ambassador to China, and Dennis C. Blair, the former director of national intelligence, suggested allowing American companies to retaliate against Chinese hackers on their own.

This emergence of cyberhawks in both nations raises the odds of a hack’s becoming a cyberwar. These voices could pressure both nations to treat any escalating cyberconflict as a latter-day Cuban missile crisis.

But the cold war model of a struggle with calibrated boundaries, clear rules, and the threat of mutual assured destruction simply doesn’t fit cyberspace.

The first major difference is terrain. The United States and the Soviet Union fought for global influence, manning divisions here and infiltrating covert operatives there. The Internet is more fluid. Neither the United States nor China can slice cyberspace into the reassuring structure of spheres of influence. With no obvious borders for states to violate or defend, power in cyberspace is at once easier to exercise and harder to maintain, a battle of subtleties rather than hard-nosed deterrence.

There are also more players today. The United States and the Soviet Union were the world’s unmatched nuclear powers. But in the cyberrealm, the United States and China stand only just ahead of other nations, hacker groups and individuals in their ability to inflict damage. And all of these actors can hide behind layers of networks and third parties, making it difficult to discover not only who attacked but also how and when. There will, in most cases, be plausible deniability. Even if American and Chinese policy makers wanted to manage the Web as carefully as their predecessors did the cold war, no working group could tame this instability.

With nations still navigating how to interact on the Web and arguments persisting about whether international law applies to the Internet, there are few established customs of cyberbehavior, legal or implicit. The United States should not expect China to follow the rules of a previous era. The norms of American-Soviet conflict, which themselves emerged out of years of gunpoint diplomacy, can’t be grafted onto cyberspace.