This book constitutes the refereed proceedings of the 4th International Symposium on Cyberspace Safety and Security (CSS 2012), held in Melbourne, Australia, in December 2012. The 30 revised full papers presented together with 7 invited talks were carefully reviewed and selected from 105 submissions. The papers cover the following topics: mobile security, cyberspace attacks and defense, security application adn systems, network and cloud security, wireless security, security protocols and models.