Microsoft warned on Wednesday that Chinese state-sponsored hackers had compromised “critical” U.S. cyber infrastructure across numerous industries with a focus on gathering intelligence.

The Chinese hacking group, codenamed “Volt Typhoon,” has operated since mid-2021, Microsoft said in an advisory. The organization is apparently working to disrupt “critical communications infrastructure between the United States and Asia,” Microsoft said, to stymie efforts during “future crises.”

The National Security Agency put out a bulletin on Wednesday, detailing how the hack works and how cybersecurity teams should respond.

The attack is apparently ongoing. In an advisory, Microsoft urged impacted customers to “close or change credentials for all compromised accounts.”

U.S. intelligence agencies became aware of the incursion in February, around the same time that a Chinese spy balloon was downed, the New York Times reported.

The infiltration was focused on communications infrastructure in Guam and other parts of the U.S., the Times reported, and was particularly alarming to U.S. intelligence because Guam sits at the heart of an American military response in case of a Taiwanese invasion.

Volt Typhoon is able to infiltrate organizations using a unnamed vulnerability in a popular cybersecurity suite called FortiGuard, Microsoft said. Once the hacking group has gained access to a corporate system, it steals user credentials from the security suite and uses them to try to gain access to other corporate systems.

The state-sponsored hackers aren’t looking to create disruption yet, Microsoft said. Rather, “the threat actor intends to perform espionage and maintain access without being detected for as long as possible.”

Infrastructure in nearly every critical sector has been impacted, Microsoft said, including the communications, transport, and maritime industries. Government organizations were also targeted.

Chinese government-backed hackers have targeted critical and sensitive information from U.S. companies before. Covington and Burling, a prominent law firm, was hacked by suspected Chinese state-sponsored hackers in 2020.

In a joint statement with international and domestic intelligence services, the Cybersecurity and Infrastructure Security Agency warned that Chinese attacks pose a continued risk to American intellectual property.