https://www.bleepingcomputer.com/news/security/microsoft-shares-how-solarwinds-hackers-evaded-detection/

Microsoft today shared details on how the SolarWinds hackers were able to remain undetected by hiding their malicious activity inside the networks of breached companies.

This previously unknown information was disclosed by security experts part of the Microsoft 365 Defender Research Team, Microsoft Threat Intelligence Center (MSTIC), and Microsoft Cyber Defense Operations Center (CDOC).