The declaration of Il-muk is never done lightly, and is always kept as a last resort. Only a Kax'Vee (or above) can declare Il-muk, though a similar state can be inflicted by a Vee or Kax'Ves on a temporary basis. This is often done as a deterrent for bad behavior by a brother.
Upon the declaration, all protections of the offender bestowed upon him by affiliation, are removed. He is no longer protected by the organization/group and can be accosted, assaulted, robbed, raped and even murdered without retribution by the group.
A Kax'Vee or greater can reverse an Il-muk declaration but this is almost never done; the Il-muk must do something incredible for the group for this to happen. Like a magic on/off switch, the Il-muk instantly becomes part of the group again, and all is forgiven. The others are not likely to return stolen items, however.
Until recently, no one had ever, to anyone's knowledge, ever been revoiced. Not until it happened to Durga "Ghost" Bloodfist. Ghost was declared Il-muk by the Sparkling Sky Cartel's Godmother (and his Kax'Vee) Lorna Sparklingsky, for fraternizing with elves. When the elves betrayed their own to warn the Sparkling Sky Cartel of the imminent attack, Ghost was forgiven and welcomed back. That was less than 15 years ago. Until then, it was just never considered.
Transmission & Vectors
The state of Il-muk can only be forced on an individual by his leader, there is no way to transmit it to someone else.
Breaking the rules of the organization, usually repeatedly, can cause the offender to be declared Il-muk.
If the Il-muk does something to prove himself to his organization before he is killed, the condition can be reversed by the one who declared it, or one of their superiors (if any). Aside from that, there is no way for the afflicted to treat themselves for this condition.
Left long enough, the Il-muk will probably die. No goblin of his organization will help him in any way, and they frown on others helping him, so if you want to stay on the goblin organization's good side, you'll ignore the Il-muk too.
Il-muk can affect any goblin or half-goblin that belongs to any sort of goblin group with a Kax'Vee.
For as long as Goblins have gathered in warrens, this condition has existed. Goblin legends say the First Chief made the first Il-muk declaration, against his General, and right hand. Since then, goblin leaders everywhere have used the declaration of Il-muk to punish the serious transgressors within their organizations.
Culturally, the Il-muk is treated lower than a chattel slave, who at least has the right to not be killed. Goblins can be malicious and many will goad their leaders into the declaration, just to be able to rob someone, and beat them up.