A headhunt is the name for hiring a strong player to attack an enemy.
You need to notify a GO when a headhunt is taking place, or it may be considered as pushing.
You cannot hire a strong player to launch IPMs ( Interplanetary Missile ) for you as that does not count as an attack. Paying a higher ranked player to launch IPMs for you counts as pushing.
A good place to hire hunters or advertise yourself as a hunter would be the Ogame board. When a hunt is complete, you need to PM the moderator of the Ogame forum.
When members from alliances get attacked they ask for help on fighting back.