A top White House official on Wednesday said at least eight US telecom firms and dozens of nations have been impacted by a Chinese hacking campaign.

Deputy national security adviser Anne Neuberger offered the new details about the breadth of the sprawling Chinese hacking campaign that gave officials in Beijing access to private texts and phone conversations of an unknown number of Americans.

Neuberger divulged the scope of the hack a day after the FBI and the Cybersecurity and Infrastructure Security Agency issued guidance intended to help root out the hackers and prevent similar cyberespionage in the future.

White House officials cautioned that number of telecommunication firms and countries impacted could still grow.