The Salt Typhoon cyberespionage operation, linked to China, targeted AT&T and Verizon systems, but both carriers report their networks are now secure, Reuters news report said.
AT&T stated no ongoing activity by nation-state actors and confirmed only a small number of individuals of foreign intelligence interest were targeted.
Verizon reported no recent threat actor activity and confirmed containment of the incident with validation from an independent cybersecurity firm.
U.S. officials identified a ninth unnamed telecom company compromised by the hackers, who reportedly gained broad access, enabling geolocation and recording of phone calls.
The U.S. Cybersecurity and Infrastructure Security Agency recommended senior officials adopt end-to-end encrypted apps in response to the attack.
Targets of the operation included individuals connected to U.S. presidential campaigns, prompting concern about vulnerabilities in communications networks.
Chinese officials denied the allegations, calling them disinformation, while U.S. agencies and telecom companies continue to investigate and mitigate the impact.
