Windows Vista is the result of over four years of work and the investment of many billions of dollars. It is billed as the most secure version yet of the Microsoft Windows® operating system. This paper discusses not only the security technologies employed by Microsoft that justify this accolade but also how, in combination, these technologies mitigate specific classes of threats. This paper presents a high-level summary of Symantec’s research findings into the security of Windows Vista, and a set of conclusions that discuss the exposure that remains even in the face of its new security technologies. The intent of this paper is not to detract from the improvements that Microsoft has made, but rather to provide an objective and balanced view of how Windows Vista will affect the overall threat landscape. Symantec started researching Windows Vista in 2005 and has monitored its development carefully. The goal of this research has been to understand the technology improvements being made by Microsoft and also to understand the threats facing the new operating system and, in turn, Symantec’s customers.