In recent years, both academia and industry in cyber security have tried to develop innovative defense technologies, expecting that to change the rules of the game between attackers and defenders. The authors start by analysing the root causes of security problems in cyberspace: (i) vulnerabilities in cyber systems are universal; (ii) current cyber systems are static, predictable and monoculture which allows adversaries to plan and launch attacks effectively; (iii) existing techniques cannot detect and eliminates attacks employing unknown vulnerabilities. Based on their analysis, they develop a novel defense framework, mimic defense (MD), that employs ‘dynamic, heterogeneity, redundancy (DHR)’ mechanism to defense cyber attacks.