"They now believe the hackers from a group called “Salt Typhoon,” closely linked to China’s Ministry of State Security, were lurking undetected inside the networks of the biggest American telecommunications firms for more than a year.
They have learned that the Chinese hackers got a nearly complete list of phone numbers the Justice Department monitors in its “lawful intercept” system, which places wiretaps on people suspected of committing crimes or spying, usually after a warrant is issued."
Salt Typhoon Wikipedia