Fantastic reporting by @kimzetter here - a year long report into what went down with #Solarwinds.
I'd like to highlight this bit. Zero trust, my arse. Lots of new details in this report. https://www.wired.com/story/the-untold-story-of-solarwinds-the-boldest-supply-chain-hack-ever/
While investigating (and not finding) the Solarwinds incident in mid-2020, Mandiant installed Solarwinds and infected its own internal network.
Also, I don't have my Twitter thread on TeamCity any more for obvious reasons, but it confirms what happened there.
I agree with Chris Krebs that it's part of a broader listening infrastructure (both Russia and China have this capability live - part of the reason I dispute the branding from MS about being the biggest cyber attack of all time is Russia aren't the only ones doing this stuff).
Btw, SolarWinds was one of the topics I got told to stop tweeting about while at Microsoft, and told not to talk about after I left.