A knife can be used with surgical precision at one particular location.
A poison can be used in a structure which constitutes a wholeness 'beneath' one's own.
Viruses are useful in situations which extend beyond a particular locality of one's consciousness.
How are viruses used?
Create a small poison structure carrying the desired energy-frequency, and set it in motion. Let it iterate and multiply.
Then, sit back and watch.
The energy it is keyed to and the energy it is carrying superimpose and vibrate with dual-frequencies for a while.
Sooner or later, balance kicks in, and you have something New.
If your virus is vastly perpendicular (irrelevant) to the system or of lesser balance than the system, it becomes extinct.
It may prove interesting to watch existing viral structures. Their flow; movement, evolution, and extinction.