"Microsoft's GitHub is hosting the leaked source code (which probably got sucked into Copilot and every other AI under the sun as a result)." "However, I don't think copyright lawyers will care. «They're also committing a crime» doesn't mean you're free to do what you want. That applies especially in ReactOS vs MS, because if ReactOS succeeds, it will compete directly with Microsoft."

And ReactOS uses GitHub Copilot: https://github.com/reactos/reactos/pull/8516

There's also such thing as being responsible (for an outcome), which in case of litigation means being culpable. Microsoft here is the sole actor that has any control on the GitHub Copilot, on what it was fed with, and thus - on its output (which would be the base of their accusation if they sue). How do you imagine such a case could be made to look like it would have any legal standing?