This book constitutes the proceedings of the 18th International Conference, CISIS 2025, held in Salamanca, Spain, during October 16&17, 2025. The 17 full papers included in this volume were carefully reviewed and selected from 36 submissions. The papers cover the following topical sections: Malware & Intrusion Detection; Cryptography & Blockchain Security; and AI Safety, Privacy & Trustworthy Systems. The papers also include the special session: Artificial Intelligence for Protecting the Internet of Things.