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You are posting false information and using fallacies which I utterly despise.
You are wrong.
Just because YOU can't manage a windows system / network properly, it doesn't mean that it is not possible.
While i agree that it takes way more effort to create a somewhat secure system running windows, it is - by far - not impossible.
We would have all of your governments and any other critical infrastructure compromised already.. The majority is using windows only..
You should keep away from the thought that not a single person can do things which YOU can't do..
You shouldn't take it to the extremes. Linux is much more secure by default, but its not perfect. It also depends on distro, some are more security oriented than others. Windows on the other hand, can be made safer, with work, but the end result isn't perfect either, and is not as good as a truly secured linux or bsd. You just can't do anything about secret backdoors/bombs/bugs hidden in code you have no access to, that is a fundamental difference you have to always live with when using closed source proprietary software.
Of course there is a lot of money to be made in this sector, some people are fool enough to insist on using windows and beg professionals to make it safer. One of the things usually done is put a firewall (with a secure os) in the gateway to the wild savage internet and their little windows Lan to at least contain the brunt of the attacks. You can also spend a lot of effort and time trying to secure as best as you can windows, within the limitations no access to the code will never let you surmount.
The irony here is that a simple user isn't going to make it, that is why they hire you in the first place. If windows was "secure by default", you would have to do a different job. And these are the typical targets, remember? Laziness.
Easy to use, easy to crack, you could say.