Singapore Telecommunications, Singapore’s largest mobile carrier, was breached by Chinese state-sponsored hackers this summer as part of a broader campaign against telecommunications companies and other critical infrastructure operators around the world, according to two people familiar with the matter.

The previously undisclosed breach was discovered in June, and investigators believe it was pulled off by a hacking group known as Volt Typhoon, according to the two people, who asked not to be identified to discuss a confidential investigation.

Officials in the United States, Australia, Canada, the U.K. and New Zealand — the "Five Eyes” intelligence-sharing alliance — warned earlier this year that Volt Typhoon was embedding itself inside compromised IT networks to give China the ability to conduct disruptive cyberattacks in the event of a military conflict with the West.