Virtual properties can refer to any resources that are under the powers-that-be control. Virtual properties include virtual objects, avatars as well as user accounts in their entirety. The common characteristics can be found in virtual economy which is as below. That lack one or more of these characteristics for virtual property still should be interpreted with reasonable flexibility. These characteristics are rivalry, persistence, interconnectivity, secondary markets, and value added by users. These elements in total create an economy system which is similar to that counterpart in real economy. Therefore, economic theory can be used in these virtual worlds.