This book constitutes the refereed proceedings of the Pacific Asia Workshop on Intelligence and Security Informatics, PAISI 2012, held in Kuala Lumpur, Malaysia, in May 2012 - held in conjunction with the Pacific Asia Conference on Knowledge Discovery and Data Mining (PAKDD 2012). The 8 revised full papers and the 8 revised short papers presented together with 1 keynote lecture were carefully reviewed and selected from numerous submissions. The papers are organized in topical sections on terrorism informatics and crime analysis, social media, intrusion detection, data and text mining, as well as information access and security.