Buying and selling online is inherently insecure. Misuse of an individual's persol information is now the leading concern among those who engage in e-commerce. This book examines privacy and security issues in online auctions. Various auction fraud issues are investigated, and several novel counter measures proposed. An online auction server was constructed to aid in developing these security measures. This allowed investigation and testing in a controlled environment. The research results include: - A complete model for conducting secure and anonymous online auctions; - A complete model for conducting secure and anonymous online share trading; - Autonomous bidding agents which bid maliciously. (Used to test the ability of the proposed security mechanisms.); - A method for detecting a fraudulent bidding practice referred to as shill bidding; and - Several alterte proposals for auction clearing algorithms. The proposed security mechanisms have been implemented on the online auction server. Results are given as simulated and practical tests. In addition, the auction server's software design is documented. Many of the techniques discussed in this research can be readily applied to commercial online auctions.