I’m very doubtful but not entirely convinced it’s not possible to manufacture a viral bio-weapon.
But the level difficulty in getting something so tiny to do exactly what you want it to (even chaotically) is another?
If anybody could harness that type of nano-technology they would rule the world (so it does not kill them to), that’s where doubt has its place?
Viruses are more like tiny machines than a living bacteria which are much easier to kill, viruses simply duplicate themselves using whatever biomaterial available but why?
They really serve no purpose other than to put whatever it is that walks on dirt back in the ground when it becomes over-populated?
When any species has many members that don’t reproduce, that promotes the existence of the species hundreds of years into the future if not thousands of years. The more reproduction you have the more likely that species becomes extinct (over-population; environment and resources cannot be sustained) and that may be the role of a virus?