This book presents refereed proceedings of the Second International Conference on Advances in Cyber Security, ACeS 2020, held in Penang, Malaysia, in September 2020. Due to the COVID-19 pandemic the conference was held online. The 46 full papers and 1 short paper were carefully reviewed and selected from 132 submissions. The papers are organized in topical sections on internet of things, industry 4.0 and blockchain, and cryptology; digital forensics and surveillance, botnet and malware, and intrusion detection/prevention; ambient cloud and edge computing, wireless and cellular communication; governance, social media, mobile and web, data privacy, data policy and fake news.