This book constitutes the refereed proceedings of the First International Workshop, IOSec 2018, sponsored by CIPSEC, held in Heraklion, Crete, Greece, in September 2018. The 12 full papers presented were carefully reviewed and selected from 22 submissions. They were organized in topical sections named: Critical Infrastructure Cybersecurity Issues; CyberSecurity Threats, Assessment and Privacy; and Vulnerability and Malware Detection.