washington —  China-linked hackers targeting key sectors of the U.S. economy appear to have been hiding in key computer systems and networks for at least five years, according to a new warning from the United States and key allies, who urge companies to take urgent action to mitigate the risk. The cybersecurity advisory issued Wednesday by multiple U.S. agencies, including the FBI and the Cybersecurity and Infrastructure Security Agency (CISA), states that a cyberthreat group known as Volt Typhoon has been “positioning itself to launch destructive cyberattacks that would jeopardize the physical safety of Americans.” In particular, the advisory warns that China-linked Volt Typhoon hackers have successfully infiltrated the computer networks of private companies linked to critical sectors of the U.S. economy, including communications, energy, water and wastewater, and transportation. The advisory further warns that Volt Typhoon hackers have been “maintaining access and footholds within some victim IT environments for at least five years.” And CISA acknowledged the penetrations may be more extensive than is currently known. Officials said other industries, including construction, information technology …