This is another one of those things that is just stupid to answer.
Because the mad scientist can't exist unless the collective consciousness of the world wants a reset. (remember the flood of Noah?)
So, what would happen if this mad scientist unleashed it, is really nothing. A freak rain storm wipes it out. Or a freak heat wave. Or it hits a small village, which dies, but no one leaves to spread it.
Further, the spread of the disease is weird. Flu viruses often spread world wide within a month. And things that you would also think should spread world wide, don't.
So, since The US are mad scientists and working on this very thing in remote bases in third world countries, we should put a stop to it. However, while there are people who think that war, or killing the "enemy" is the way to stay safe, then there will always be this research. Thus, you really have to heal these people's fears/pain. And you should keep such people out of power.
Next, there are so many ways to look into the human body. Many in the area of naturopathy medicines have fantastic methods of just looking through the body. So that the person with the code could easily be found. And then, we could probably read the code without opening the person up.
edit: I forgot to say why this is stupid to answer. What this does is it makes you paralyzed to living life. Every action has/could have dire consequences. The only way forward is to deal with the very high probability ones, and then just do your best in each moment to do no harm.
And killing someone else, to stop someone else from killing them is stupid.