Security requirements for pervasive computing environments are different from those in fixed networks. This is due to the intensity and complexity of the communication between the user and the infrastructure, the mobility of the user, and dynamic sharing of limited resources. As pervasive computing makes information access and processing easily available for everyone from anywhere at anytime, the close relationship between distributed systems and mobile computing with a pervasive infrastructure leads us to take a closer look at different types of vulnerabilities and attacks in such environments. Pervasive computing includes numerous, often transparent, computing devices that are frequently mobile or embedded in the environment, and are connected to an increasingly ubiquitous network structure. For example, when an organization employs pervasive computing, the environment becomes more knowledgeable about the users’ behavior and, hence, becomes more proactive with each individual user as time passes. Therefore, the user must be able to trust the environment and the environment must be confident of the user’s identity. This implies security is an important concern in the success of pervasive computing environments. In this chapter we evaluate the suitability of existing security methods for pervasive environments.