When you attack or hack an enemy portal in Ingress, the portal will ZAP you for XM damage. The amount of damage is dependent on the level of the portal, not the level of the resonators in there, and is documented.
I have been unable to find more information about portal ZAP range, or other attack properties, though.
What is the ZAP range of a portal? Is there is limit to the firing rate or the firepower of a portal, or will it always ZAP you for any attack/hack?