But what happens when...
...malware propagation rates start to exceed the rate by which they can be scanned? I'm surprised writers haven't taken more pages from amoebae and tried things like "code conjugation" in which two different strains detect each other and swap code pieces, thus turning themselves into two new, unknown strains instantly and without any human intervention. If new strains can be created without human intervention, then it's probably safe to say the malware war will be well and truly lost--nature itself shows how resilient such things as insects, amoebae, and bacteria have been despite eons of antagonism and predation.