Viruses are used to kill a large number of a specific creature over an area. Their target is decided by the DNA the player puts into the virus. Potency and infectiousness may be upgraded by spending turns if you have a Bio-Warfare Center.
First you need to scout the player you wish to attack, determining the creatures they are using, and picking a creature to target.
By pressing the white button in the upper left hand corner of the DNA viewer you can see which basic DNAs the creature is composed of. Simply use the same creatures in the same stats to make a virus specific to this creature.
This is the killing efficiency of the virus. The potency is the percentage of creatures killed, i.e. a potency of 100 will kill 100% of that creature, 50 potency kills 50% etc. Increasing potency requires a BioWarfare center
There is no need to raise the potency over 100. If this is done and the virus is used, the report will actually show a greater amount of creatures killed by it than there were to begin with - although the result is the same.
The turns used increase potency are (complexity * 5)/point.
Complexity is just based on total number of creatures used in the virus.
This is the range of the virus, by having a large infectiousness you can take out the creatures of many players opening up many for attacks. Infectiousness cannot exceed 99, and turns will be lost if too many are invested (at least until this is fixed). Increasing infectiousness requires a bio-warfare center.
Like potency the turns used are (complexity * 5)/point.