What you may not be taking into account is that a *lot* of people _have_ moved from Windows to Linux - primarily the server sector. It's naive to think that Linux has survived under a "security by obscurity" blanket just because it's not on desktops.
And - many of these servers are actually a lot *more* visible than the Windows machines, as they generally don't have IP addresses that change on a whim, sit behind as many layers of routers & firewalls (for at least the directly-connected Internet-based servers) and whatnot.
Linux is out there - arguably *more* than Windows when you consider all the servers, routers, phones, even toasters that run it; and considering that over the last 20+ years this is the number of viruses (give or take) for Linux: http://en.wikipedia.org/wiki/Linux_malware#Viruses ... Linux is definitely more secure.
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