At some point, computer systems will be more like biologic systems - they will just carry a more or less permanent "flora" of parasites, that will have to be tolerated unless they become explicitly hostile.
Any sufficiently complex system will exhibit this trait sooner or later.
That's an interesting way of looking at "parasitic" programs. Maybe we could even get those parasites to work for us, like trapping them as the house pen-tester. You could employ the constant barrage of attempted ssh logins as remote connectivity check or something.
Any sufficiently complex system will exhibit this trait sooner or later.