The last machine on my desk with no MMU was an Amiga 2000
Since malware relies on having access to the whole computer in order to do harm when the code is executed, malware on such a machine will be defeated, because even if it manages to get into the machine as a bona fide piece of code, as soon as it runs, it will find it has no direct access to anything except an area of RAM. It can’t mess with the operating system because it will run in user mode. It can’t mess with the mass storage because only kernel processes can reach the physical addresses of peripherals.
It seem the author has totally bypassed any knowledge about how modern computer systems or even malware actually works and is making things up as he writes? It's like listening to a neocon explaining the political situation in the Middle East and how we need to smash in some doors lest people get uppity etc.
I recommend taking up a good old Tanenbaum explaining principles of Operating Systems. Then to start studying practical examples of how security is being bypassed by various means in case the system is not kept at minimal levels of complexity with a strictly enforced and mathematically describable security policy with no bugs in the code underlying it. These systems are very rare, very restricted in functionality and the hoi polloi doesn't want them.
The combination of kernel and user register sets in the CPU with hardware memory management and a small amount of hard-wired logic that no software of any kind could circumvent, meant that with a competent operating system, these machines were essentially bomb proof.
Bomb proof my arse: Morris worm says no. Oh you mean it needs to run VMS? Right.