Windows sources have escaped before. I doubt that Windows is buildable outside of Microsoft (and the bits are definitely not signable, since you need access to a key vault for that).
Useful for research, and finding security issues. Not much else.
Useful for research, and finding security issues. Not much else.
You can break patents without ever knowing the patent existed. So looking at this code wouldn't trigger a new patent problem.
And simply looking at some code, closing it, then later writing code that does the same functionality is not breaking copyright. So looking at this code would not trigger copyright.
Not a lawyer, though, but a quick search confirms this.