Were it not for Windows' long-standing installed base and overwhelming market dominance, it seems unlikely that anyone would argue seriously for the merit of the operating system, plagued as it is by high prices, security problems and vendor lock-in.
The Mac might enjoy a smaller installed base than Windows does, meaning there's less of the monoculture effect and less of a lure for malicious hackers, but Linux blows them both away when it comes to security.

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