Linux is more secure than windows... Why?
A) Users are not automatically 'administartors' called 'root' in linux when the operating system is installed, so major changes to the operating system cannot be made without a user name and root password.
B) Linux does not run with executable files like windows. There is a bit of tech knowledge required to install a lot of programs (this is changing with the 'app' culture, but most apps are pretty well regulated), unlike windows that you click on an executable and it installs automatically - if you miss unticking boxes you can install viruses and other malware in hidden toolbars and add-ons.
C) Linux is far more cutomizable. Go to distrowatch.com and see how many linux distributions there are based on a core linux kernel (ie Debian, red hat, Arch etc). This can make it far harder to hack.
D) It is free with the GNU licence, most apps and programs are free, so to attck with malware is not generally the 'done thing'. It happens with windows and apple (very rare on apple as its OS is based on Unix) products as they are massive commercial entities which brings out the hackers, a lot who try things , are against the money making and various other reasons.
E) Windows uses a pretty insecure browser as standard that is prone to toolbars, malicous addons such as search engines. Linux default is Firefox, which is fra more secure.
These are some reasons I have observed and there are more reasons which are beyond my knowledge scope. Most of all though security on an operating syste is mainly down to you and how you use it.