The disclosure is the latest sign that the Chinese burrowed deep inside U.S. communications networks in a far-reaching espionage campaign.

An FBI investigation into reported hacks at AT&T and Verizon reveals 'a broad and significant cyber espionage campaign,' the agency says.

The U.S. government has confirmed that hackers with links to China breached multiple U.S. telecommunication service providers to access the wiretap systems used by law enforcement to surveil Americans.