Suspicious behavior on T-Mobile US Inc.’s network devices tipped off the company to a breach that was potentially part of a sprawling cyber-espionage campaign that has raised urgent questions about the exposure of a critical sector of the economy.

T-Mobile says the Chinese "Salt Typhoon" hackers who recently compromised its systems as part of a series of telecom breaches first hacked into some of its routers to explore ways to navigate laterally through the network.

This morning, a report from Bloomberg states that T-Mobile engineers spotted suspicious behavior on the carrier's network devices that tipped off the carrier that it was under attack. Jeff Simon, T-Mobile 's chief security officer,

T-Mobile has joined the growing list of US telecom operators who have been breached by Salt Typhoon. The company confirmed in a statement to the Wall Street Journal that while a breach had occurred, there was no evidence to suggest the attackers had accessed or exfiltrated any customer data.

T-Mobile has severed its connection to the unnamed wireline provider, which it suspects may still be compromised.

The mobile carrier provided its first detailed rundown of how it stopped hackers from infiltrating its networks.