In recent years, interactive virtual environments such as Second Life, and virtual globe applications such as Google Earth, have become very popular. However, delivering massive amounts of interactive content to millions of potential users brings enormous challenges to content providers. Distributed peer-to-peer (P2P) approaches have thus been proposed to increase the system scalability in affordable ways. Building content delivery systems based on P2P approaches nevertheless creates security concerns for commercial vendors. This paper presents a generic system model for subscription-based service providers to adopt P2P-based, non-linear streaming for interactive content. We also propose solutions to the issue of content authentication, such that paying customers can be sure of the authenticity of the content retrieved from other users. Other practical security issues in an extended system model are also identified to allow further investigations in this problem space.