Along with the trend in networked computing environments towards largely unbounded network infrastructures, the traditional anti-sniffing issue meets a great challenge. This paper presents a distributed anti-sniffing approach in which varied anti-sniffing methods including protection methods, detection methods and countermeasure methods are integrated smoothly. This idea is also valuable for solving other security problems of unbounded networks. KEYWORDS Anti-sniffing, Unbounded network, XML, Message, Policy