Anarchy Online Extreme

Protection

All armor class skills are not true skills in the sense of the word. You will normally not be able to increase them by any other means than wearing armour or using a nano formula specifically designed for the task.

Impact and Projectile Weapons AC
Defines how much damage is reduced from the physical impact of projectile weapons, or any other object with sufficient velocity.

Energy Attack AC
Defines how much damage is reduced from energy attacks.

Melee and Martial Arts Attack AC
Defines how much damage you can avoid from melee and martial arts attacks.

Cold AC
The rest of the protection skills are true skills, and raising them will reduce the amount of damage taken from the designated situations. The Cold damage AC increases the amount of cold damage you can take. It also increases chances of resisting nano based cold damage.

Fire AC
This skill defines how much fire based damage your character will be able to resist.

Chemical AC
Chemical AC defines how much chemical contamination your character can be subjected to without dying. Poison can also be found in this category.

Radiation AC
Is the indication of how much radiation you can resist.

Disease AC
Defines the amount of contamination you can take before getting sick.

Nano Resistance
Is the indication of how well you and your nano containment unit (NCU) resist, and totally avoid hostile nano programs running on your system. This is a very important skill for any profession and is 80% dependent on psychic and 20% on intelligence.

Source: Official Anarchy Online Page