If Microsoft/Apple are working with the NSA they can hide commands in the code to operate without you. There were already NSA secret keys found in Windows.
The reason Windows is used by most of the world is because it's easier. It's not better, just easier, because the company profited by making it user friendly. Meanwhile the open-source community is not paid, but if enough people show an interest in using Linux regularly more user-friendly development would happen. Until then it's a problem. Yes, Ubuntu is Linux and probably safe, but Fedora is more certainly safe because none of it is closed source.
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