That hardly constitutes a rebuttal.I see this sort of thing from the Tin Foil Hat crowd over here in the US, who think Microsoft is in league with the NSA, and has left back doors in Windows so the NSA can snoop on their PCs. All I can say is "You wish you were important enough that anyone could be bothered to snoop on your computer!"
One OS gets used on 90% or so of the world's computers. Are you certain DHS et. al. have no interest in having a back door in it, even though a given random individual holds no interest for them? Some Windows users in the world are interesting to them.
I have no proof one way or another, but human nature being what it is, I'd bet a fair amount DHS does have a back door into Windows.