THE ISLAND of Guam, a tiny American territory that lies more than 6,000km west of Hawaii, has long known that it would take a battering in any Sino-American war. The island’s expanding airfields and ports serve as springboards for American ships, subs and bombers. In the opening hours of a conflict, these would be subject to wave after wave of Chinese missiles. But an advance party of attackers seems to have lurked quietly within Guam’s infrastructure for years. In mid-2021 a Chinese hacking group—later dubbed Volt Typhoon—burrowed deep inside the island’s communication systems. The intrusions had no obvious utility for espionage. They were intended, as America’s government would later conclude, for “disruptive or destructive cyber-attacks against…critical infrastructure in the event of a major crisis or conflict”. Sabotage, in short.

For many years, Sino-American skirmishing in the cyber domain was largely about stealing secrets. In 2013 Edward Snowden, a contractor, revealed that the National Security Agency (nsa), America’s signals-intelligence agency, had targeted Chinese mobile-phone firms, universities and undersea cables. China, in turn, has spent decades stealing vast quantities of intellectual property from American firms, a process that Keith Alexander, then head of the NSA, once called the “greatest transfer of wealth in history”. In recent years this dynamic has changed. Chinese cyber-espionage has continued, but its operations have also grown more ambitious and aggressive. Russia, too, has intensified its cyber-activities in Ukraine, with Russia-linked groups also targeting water facilities in Europe. These campaigns hint at a new era of wartime cyber-sabotage.