re:I agree, however, that there should be a word which describes relentless intermittent persistence ... like a viral infection which succumbs to a new vaccine but mutates and comes roaring back years later, as virulent as ever.

the shortest way i know to express that is 'red queen theory'--from the red queen's comments in Alice in wonderland--'you have to run as fast as you can just to stay in place, and even faster if you want to get ahead'

its applied to all sorts of 'evolutionary' programs.. the idea that you have to keep outrunning (evolving as fast as you can) 'adversaries' just to keep alive..

analogy works for living things and 'technology' alike.