It's safe to assume that Windows is backdoored, as it's closed, not audiatable and is a part of PRISM. It's not a proof, but this is how good opsec works.
And yes, this is not equivalent to what the parent said, but your reaction should be similar.
I would put my money on that these leaks have full source code. Also, currently, Windows even AFAIK sends keystrokes to the US, where NSA has full access to any company whenever they need by the law, with no oversight. No backdoors are required.
