Voice over IP telephony is gaining popularity quickly, and is often replacing traditional PSTN connectivity due to its low cost and easy implementation. In moving from a legacy PSTN system to a newer technology such as VoIP, security is often overlooked by vendors and users. This can present a significant problem in the corporate environment, where security in terms of both privacy and service is a key requirement. For residential users, credential theft can result in a significant annoyance, such as toll fraud or identity theft. This book focuses on attacks that compromise privacy, and details methods of detecting and mitigating these attacks. IPSec is used to ensure that signalling and media traffic are unable to be intercepted. These techniques should help administrators of networks carrying voice traffic to implement necessary measures to ensure that security and privacy remain intact. They should be particularly useful in corporate environments, where sensitive information needs to remain inaccessible to anyone other than its intended recipients.