China has hacked into American power grids and companies for decades, stealing sensitive files and intellectual property such as chip designs as it seeks to gain an edge over the United States.

But a sweeping cyberattack by a group known as Salt Typhoon is China’s most ambitious yet, experts and officials have concluded after a year of investigating it. It targeted more than 80 countries and may have stolen information from nearly every American, officials said. They see it as evidence that China’s capabilities rival those of the United States and its allies.

The Salt Typhoon attack was a yearslong, coordinated assault that infiltrated major telecommunications companies and others, investigators said in a highly unusual joint statement last week. The range of the attack was far greater than originally understood, and security officials warned that the stolen data could allow Chinese intelligence services to exploit global communication networks to track targets including politicians, spies and activists.

Hackers sponsored by the Chinese government “are targeting networks globally, including, but not limited to, telecommunications, government, transportation, lodging, and military infrastructure networks,” the statement said.

British and American officials have described the attack as “unrestrained” and “indiscriminate.” Canada, Finland, Germany, Italy, Japan and Spain were also signatories to the statement, which was part of a name-and-shame effort directed at the Chinese government.

“I can’t imagine any American was spared given the breadth of the campaign,” said Cynthia Kaiser, a former top official in the F.B.I.’s cyber division, who oversaw investigations into the hacking.