System, method and computer program product for verifying an avatar owner as a human user of an avatar in a virtual world environment in which humans interact through avatars via client devices in network communication with a server device. A request for challenging an avatar in the virtual world environment is received to determine whether that avatar is controlled by an application program user (bot). A user client device associated with a challenged avatar is identified and a Human Identification Proof (HIP) message for detecting a human user versus a bot controlling the challenged avatar is generated and communicated, for receipt at the identified user client device. It is determined from the response, whether the user is a bot or a human user. If a challenged avatar is determined to be a bot, then the server device prevents the challenged avatar from further interaction in the virtual world environment.