If your base is attacked, the structures will suffer no damage. However, your base defences and any fleet you have at that base will attempt to protect your base, and can be destroyed (does not include defenses) or damaged. If the attack is successful, they occupy your base they recieve 30% of your base income each hour. You do, however, still have full control over the base.
At a players base: (number of hours since last pillage; max 100)% * (Base Economy/Total Bases Economy) * Base Owner Credits At a NPC base: Pillage = (number of hours since last pillage – max 100)% * Base Economy * 25 Additional Pillage bonus: ½ * (base actual income-new income) * (base actual income-new income)/2 * 24