Methods and apparatus associate a computed difference factor to avatars that are to interact with one another in a simulated environment. Applying a difference factor to the avatars enables identification of similar avatars in order to avoid mistaken identities among the avatars. The difference factor predicts probability that one avatar is mimicking another avatar. An attribute uniqueness algorithm may assign the difference factor based on name, appearance, and/or accessory similarity between two avatars. A user index may be used to store data describing attributes of each avatar for analysis using programs that are stored in memory and that execute the attribute uniqueness algorithm. Further, system validation of each avatar provides ability to protect and control likeness of the avatars in the virtual world.