I am not geneticist nor do I have friends who have direct contact with CRISPR, conclusion drawn were just aggregation of data. Two years ago I remember that lab in Holland has not published a paper that was saying how to turn H1N1 or alike viruses in more viral and more deadly versions.
But, I have knowledge in information science and I can tell you that even most complex 20000 lines code can be reverse engineer or modify by any developer if you have basic understanding and appropriate tools.
Viruses are not bigger than 20000 base-pairs ... So in my mind CRISPR/CAS9 is the tool, of course one would need some additional equipment, and the knowledge.
I am not worried about idiots in their garages, I am worried about that one genius with an emotional problems.
It is just an uncanny idea.