This book constitutes the refereed proceedings of the 4th International Conference on Computational Intelligence in Security for Information Systems, CISIS 2011, held in Torremolinos-Málaga, in June 2011 as a satellite event of IWANN 2011, the International Work-conference on Artificial and Natural Neural Networks.The 38 revised full papers presented were carefully reviewed and selected from a total of 70 submissions. The papers are organized in topical sections on machine learning and intelligence, network security, cryptography, securing software, and applications of intelligent methods for security.