The Pentagon’s new 33-page cybersecurity strategy is an important evolution in how America proposes to address a top national security threat. It is intended to warn adversaries — especially China, Russia, Iran and North Korea — that the United States is prepared to retaliate, if necessary, against cyberattacks and is developing the weapons to do so.

As The Times recently reported, Russian hackers swept up some of President Obama’s email correspondence last year. Although the breach apparently affected only the White House’s unclassified computers, it was more intrusive and worrisome than publicly acknowledged and is a chilling example of how determined adversaries can penetrate the government system.

The United States’ cybersecurity efforts have typically focused on defending computer networks against hackers, criminals and foreign governments. Playing defense is still important, and the Obama administration has started to push Silicon Valley’s software companies to join in that fight. But the focus has shifted to developing the malware and other technologies that would give the United States offensive weapons should circumstances require disrupting an adversary’s network.

The strategy document provides some overdue transparency about a military program that is expected to increase to 6,200 workers in a few years and costs billions of dollars annually. Officials apparently hope talking more openly about America’s plans will deter adversaries who view cyberattacks as a cheap way to gather intelligence from more destructive operations.