1. A computer-implemented method of generating an advertisement in a virtual world interactive computer game environment, the method comprising: monitoring a behavior of a user participating in a virtual world interactive computer game environment using at least one hardware-implemented processor, wherein monitoring the behavior includes monitoring interaction of a user-controlled character within the virtual world interactive computer game environment; determining a personality trait of the user from the monitored behavior; and selecting an advertisement to display to the user in the virtual world interactive computer game environment based upon the determined personality trait of the user.