Information Abuse and Political Discourse: People Still Care About Facts: Twitter Users Engage More with Factual Discourse than Misinformation -- Extracting common features of fake news by Multi-Head-Attention -- Twitter Bots Influence on the Russo-Ukrainian War During the 2022 Italian General Elections -- Did State-sponsored Trolls Shape the 2016 US Presidential Election Discourse? Quantifying Influence on Twitter -- Attacks: Data Reconstruction Attack Against Principal Component Analysis -- The Impact of Synthetic Data on Membership Inference Attacks -- Time Is On My Side: Forward-Replay Attacks to TOTP Authentication -- Social Structure and Community: Cyber Security Researchers on Online Social Networks: From the Lens of the UK's ACEs-CSR on Twitter -- The Social and Technological Incentives for Cybercriminals to Engage in Ransomware Activities -- Security and Privacy Matters: Graph Analysis of Blockchain P2P Overlays and their Security Implications -- Secure and Efficient Data Processing for Cloud Computing with Fine-Grained Access Control -- Detection of Privacy-harming Social Media Posts in Italian -- Edge local Dierential Privacy for Dynamic Graphs -- Temporal Analysis of Privacy Enhancing Technology Trac using Deep Learning.

This book constitutes the proceedings of the 9th International Symposium on Security and Privacy in Social Networks and Big Data, SocialSec 2023, which took place in Canterbury, UK, in August 2023. The 10 full papers and 4 short papers presented in this volume were carefully reviewed and selected from 29 submissions. They were organized in topical sections as follows: information abuse and political discourse; attacks; social structure and community; and security and privacy matters. Papers "Data Reconstruction Attack Against Principal Component Analysis" and "Edge local Differential Privacy for Dynamic Graphs" are published Open Access under the CC BY 4.0 License.