AI Summary

A Chinese espionage group known as UNC5221 has been infiltrating Microsoft 365 environments with the Brickstorm backdoor and two previously undocumented malware families, Plenet and AgentPSD. Investigators found the threat actor had gained entry to the victim network at least 18 months before it was detected. The group also compromised the victim organization’s managed services provider, extending its reach within the network. The discovery highlights the prolonged persistence of the actor and the breadth of its compromise.

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