Be aware that linux security is quite overestimated.
Torvalds attitudea bug is a bugis not helping in it.
This is the reason NSA developed SELinux initially: the kernel is like an Emmentaler.
This is the reason Joanna Rutkovska [https://en.wikipedia.org/wiki/Joanna_Rutkowska] is developing Qubes OS [https://www.qubes-os.org].
This is the reason UCAVs will be deployed using a mathematically verified microkernel [https://sel4.systems/] over a predictable hardware.
Linux is not secure.
No system is really secure if you do not set it up properly. Compared to a Windows machine, or even in a lot of cases, compared to a Mac, the security potential offered in Linux is a lot more advanced. This if course assumes that you take the time to set it up properly to begin with. As I said though, any operating system isn't secure if you do not set it up properly.