If they are bad, extermination seems the wiser path and if clever people wrote virii, then they would in turn create good ones. Flagging down bad code segments in your operating system that could crash with a notify they exist or creation of jump code on demand to circumvent the bad stuff, i.e. code morphing in the current tech. Testing mass storage media and adding data to move up or compress to reductiion for block size optimization. This kind of controlled virus would be utilized most likely inside of an Oracle or some other DBMS closed environment to enhance performance. Retrovirii code would do much more sophisticated things to segments of instructions for performance, something I worked on theoretically since the 1980's.
Many parts of life have a stem rooted in virii.
Spyware is sort of virus and is made by smart people with James Bond's Q in mind. The same analogy can be stretched to the real world, people may not be realising the danger, and on even realising it they may refuse to call in the experts. The Internet security field has always been an arms race, and I think it is safe to say that theory has nearly always lead practice. Sniffing was alluded to in the original Ethernet design paper, for example. Various friends and I have sat in hottubs speculating when various Bad Things would appear in the wild, generally many years before they did.