Ninth Privacy Enhancing Technologies Symposium -- Capturing Social Networking Privacy Preferences: -- Regulating Privacy in Wireless Advertising Messaging: FIPP Compliance by Policy vs. by Design -- A Comparative Study of Online Privacy Policies and Formats -- Vida: How to Use Bayesian Inference to De-anonymize Persistent Communications -- Scalable Link-Based Relay Selection for Anonymous Routing -- Using Linkability Information to Attack Mix-Based Anonymity Services -- Physical Layer Attacks on Unlinkability in Wireless LANs -- RequestPolicy: Increasing Web Browsing Privacy through Control of Cross-Site Requests -- Enlisting ISPs to Improve Online Privacy: IP Address Mixing by Default -- Privacy-Preserving Policy-Based Information Transfer -- Privacy-Preserving Computation and Verification of Aggregate Queries on Outsourced Databases -- APOD: Anonymous Physical Object Delivery -- On the Optimal Placement of Mix Zones -- Privacy-Preserving Face Recognition.

This book constitutes the refereed proceedings of the 9th International Symposium on Privacy Enhancing Technologies, PETS 2009, held in Seattle, WA, USA, in August 2009. The 14 revised full papers presented were carefully reviewed and selected from 44 initial submissions. The papers - both from academia and industry - cover design and realization of privacy services for the internet and other communication networks and present novel research on all theoretical and practical aspects of privacy technologies, as well as experimental studies of fielded systems.