[jeroenhd]

It's possible as long as Microsoft removes all code commissioned by third parties, rewrites all copyright and trademark statements and explicitly licenses the very release that got leaked. Anything else could be seen as non-action in case of a software leak which could lead to very unfortunate results in any lawsuits that come up.

That's a lot of work for what is essentially a gross intellectual property violation as well as a leak of trade secrets.

Tk protect your trademark, you absolutely must go after trademark violations. Any build labeled "Windows" that results from this source code must be taken down if Microsoft wants to keep the trademark on things like "Windows".