The breach, traced to Chinese state-sponsored hackers, may have lasted for months, according to The Wall Street Journal.

Multiple U.S. broadband providers, including Verizon, AT&T, and Lumen Technologies, have been breached by a Chinese hacking group tracked as Salt Typhoon, the Wall Street Journal reports.

Chinese hackers accessed the networks of U.S. broadband providers and obtained information from systems that the federal government uses for court-authorized wiretapping, the Wall Street Journal reported on Saturday.

The intrusion affected major telecom company networks that cooperate with court-authorized U.S. requests for communications data, according to a recent report.

The director of the National Security Agency said Sunday a Chinese hack of three major telecommunications firms is under investigation, but it remains “premature” to discuss the case.

A highly skilled group of Chinese government-linked hackers has in the last several months infiltrated multiple US telecommunications firms in a likely search for sensitive information bearing on national security,