Virtual damage is damage that is not permanent. After about an hour has passed since virtual damage has been inflicted, the being recovers the lost stamina. Weapons that inflict virtual damage are used when the attacker wishes to keep the target alive.
The most common virtual damage (stun) weapons are lasers and blasters that have been modified to inflict virtual damage. A stun weapon will usually cost 25% more than the cost of its normal damage counterpart. Other stun weapons include toxins, grenades, and some neural weapons.
During combat, virtual damage is treated the same as normal damage in almost every respect. If you take a large hit to the head or go below 0 stamina you will have to make a consciousness roll. A being with 20 stamina, which takes 8 normal damage and 15 virtual damage will be at -3, just as if it was all normal damage.
Aside from regaining the lost stamina, the biggest difference between virtual damage and normal damage is if a being's stamina goes below -10. If a being is at -11 and has only taken normal damage then he is dead irrevocably. However, if some or all is virtual damage, then the being will still live. For each point of virtual damage below -10, it will take an additional hour of time to regain the lost stamina.
It is not possible to inflict a mortal wound with a virtual damage weapon. A medical patch will heal normal damage first, and virtual damage after.