Important note. A lot of sources are reporting that the Nx Console extension is the vector by which GitHub was compromised. Although that extension was breached concurrently with the GitHub announcement, GitHub has neither confirmed nor denied this publicly. The connection remains speculation, not fact.
GitHub's internal repositories have been exfiltrated and offered for sale.
https://discourse.ifin.network/t/github-internal-repositories-compromised-offered-for-sale/484