This book constitutes the refereed proceedings of the 9th International Conference on Digital Forensics and Cyber Crime, ICDF2C 2017, held in Prague, Czech Republic, in October 2017. The 18 full papers were selected from 50 submissions and are grouped in topical sections on malware and botnet, deanonymization, digital forensics tools, cybercrime investigation and digital forensics triage, digital forensics tools testing and validation, hacking