Five sources familiar with the incident have reported that suspected Chinese hackers exploited a flaw in SolarWinds software last year, using the vulnerability to break into US government computers. This creates a new twist to the already complicated SolarWinds Russian espionage campaign against the US government and private entities. Two individuals briefed on the case claim that FBI investigators discovered that the National Finance Center, a federal payroll agency, was among the infected organizations. This has created fear that financial data on thousands of government employees may have been compromised.

The software flaw allegedly exploited by Chinese hackers is different from the method in which the Russian government operatives utilized. Security researchers have indicated that a second group of hackers was abusing SolarWinds’ software at the same time as the Russian hack, however, the suspected China connection has not been previously reported. It is unclear how many organizations were compromised by the suspected Chinese campaign, however, the attackers used computer infrastructure and hacking tools historically deployed by Chinese state-backed cyberspies.

Read More: Suspected Chinese hackers used SolarWinds bug to spy on U.S. payroll agency