SolarWinds hackers studied Microsoft source code for authentication and email
https://www.reuters.com/article/us-cyber-solarwinds-microsoft/solarwinds-hackers-studied-microsoft-source-code-for-authentication-and-email-idUSKBN2AI2Q0
The hackers behind the worst intrusion of U.S. government agencies in years won access to Microsoft's secret source code for authenticating customers, one of the biggest vectors used in the attacks.