Emerging virtual technology suggests that we are moving into a new age of technology, Web 3.0, in which social networks and 3D virtual environments are prominent. Many new business opportunities present themselves in this context. However, business success in the new virtual world requires an understanding of how people behave in virtual worlds so that they can be effectively and efficiently managed. This paper examines how people behave in virtual worlds by using a Triandis interpersonal behavior model. The data were collected in Cyworld, and the results were tested by Lisrel 8.70. We examined two types of behaviors, giving information and obtaining information. We show that although behavioral intention plays a role in shaping virtual world behavior, habit plays a major role in determining whether people will give information and obtain information. What is more interesting is that behavior related to obtaining information is a strong antecedent of behavior related to giving information in virtual worlds. The conclusion provides several implications for both researchers and virtual world developers.