The hackers, believed to be associated with a Chinese intelligence agency, managed to infiltrate T-Mobile as part of a prolonged effort to monitor the cellphone communications of key intelligence targets. The Journal did not specify when the breach occurred.
A spokesperson for T-Mobile informed Reuters via email that the company is actively monitoring this widespread attack. They emphasized that, at present, T-Mobile's systems and data have not been significantly affected, and there is no evidence suggesting any impact on customer information.
The report from the WSJ did not clarify whether any specific information regarding T-Mobile customers' calls or communication records was compromised.
On Wednesday, the FBI and the U.S. Cybersecurity and Infrastructure Security Agency (CISA) announced that hackers linked to China had intercepted surveillance data meant for American law enforcement after breaching an undisclosed number of telecom companies.
Earlier in October, the Journal indicated that Chinese hackers had accessed the networks of U.S. broadband providers, including Verizon Communications, AT&T, and Lumen Technologies, and had acquired information from systems utilized by the federal government for court-sanctioned wiretapping.
The Chinese government has previously denied allegations from the U.S. and other nations regarding its use of hackers to infiltrate foreign computer systems.