1. A computer-implemented method for providing advertising in a virtual world, the computer-implemented method comprising computer-implemented operations for: providing, by a computer having a processor and a memory, an inventory list identifying a plurality of empty virtual objects that exist in the virtual world of a massively multiplayer online (MMO) application; receiving, by the computer, a selection of one or more empty virtual objects from the inventory list; upon receiving the selection of the one or more empty virtual objects from the inventory list, providing, by the computer, an advertisement list identifying a plurality of advertisements, the plurality of advertisements in the advertisement list being conditioned upon the one or more empty virtual objects that are selected from the inventory list such that the advertisement list excludes advertisements that the one or more empty virtual objects are incapable of displaying; receiving, by the computer, a selection of one or more advertisements from the advertisement list; upon receiving the selection of the one or more advertisements from the advertisement list, placing, by the computer, the one or more advertisements on the one or more empty virtual objects in the virtual world thereby transforming, the one or more empty virtual objects on which the one or more advertisements are not placed into one or more virtual objects on which the one or more advertisements are placed, wherein participants view the one or more advertisements by interacting with the one or more virtual objects in the virtual world via avatars controlled by the participants; wherein receiving a selection of one or more advertisements from the advertisement list comprises: receiving, by the computer, a first selection of one or more advertisements from the advertisement list; associating, by the computer, the first selection of one or more advertisements to a first set of participants; receiving, by the computer, a second selection of one or more advertisements from the advertisement list; associating, by the computer, the second selection of one or more advertisements to a second set of participants; and, wherein placing the selection of one or more advertisements on the selection of virtual objects in the virtual world comprises: placing, by the computer, the first selection of one or more advertisements on the selection of virtual objects when the first set of participants interact with the selection of virtual objects in the virtual world via a first set of avatars controlled by the first set of participants; and placing, by the computer, the second selection of one or more advertisements on the selection of virtual objects when the second set of participants interact with the selection of virtual objects in the virtual world via a second set of avatars controlled by the second set of participants.