Back in May, a host of United States security agencies issued an unusual joint statement. Hackers linked to China had infiltrated US government computer systems in the Indo-Pacific, they reported, in an attack dubbed Volt Typhoon.

For years, US cyber experts watched as similar groups carried out sophisticated commercial espionage, making off with intellectual property and other business secrets. But this was different. America’s spy agencies found Chinese technology hidden inside critical computer networks in its military facilities, including in the strategically located island of Guam.