There had been a major software security breach in the world of software management. I've been following this event in order to grasp the magnitude or scale of this breach which had ensnared public and private organizations. It does appear this security breach had affected a wide range of companies not only in the US and also agencies in the US Fed Gov as well. There was a joint write-up between Microsoft and Fireeye on how this breach was completed.
https://www.fireeye.com/blog/threat-research/2020/12/evasive-attacker-leverages-solarwinds-supply-chain-compromises-with-sunburst-backdoor.html
https://cyber.dhs.gov/ed/21-01/
https://us-cert.cisa.gov/ncas/alerts/aa20-352a
Many of the IT Security has been using security tools to decipher what was done in the code (dll) file by the following software:
https://www.fireeye.com/blog/threat-research/2020/12/evasive-attacker-leverages-solarwinds-supply-chain-compromises-with-sunburst-backdoor.html
https://github.com/cybercdh/hacks/tree/master/sunburst
https://www.winitor.com/
https://ghidra-sre.org/