[Utilizer]

You have to purposefully make a file executable before you run it, (with Linux at least).

In Linux, it does not matter if you make the file "executable" or not. The underlying instructions will go nowhere because the underlying hardware calls and system instructions are not the same or even if similarly functioned, are not processed the same way by the basic subsystems.

You can make a text file that has nothing in it but the words:
"Printtoscreen: THIS MACHINE BELONGS TO pMSNBC ctrlA&endline
EndPrinttoscreen" and make it an executable.

Nothing is going to happen. The correct machine codes are simply not there.

[WhiskeyX]

You are assuming the Cryptolocker variant attacking a Linux system was not crafted specifically to be native on a Linux kernal. Cryptolocker malware targeting the Linux kernal would of course be crafted to operate in the Linux environment. Malware access to Linux might be gained with an as yet undefended privilege escalation to root vulnerability for one hypothetical example. Once the malware has gained root access, the malware can introduce the rest of the software needed to implement a Cryptolocker function or other ransomware. Fortunately, it is normally substantially more difficult to compromise the security of a Linux system.