Cheng-Yu Chao (also known as Jeffxx) is a member of Chroot - the top private hacker group in Taiwan. He has been taking part in CTF competitions for over 10 years, is a member of HITCON and 217 CTF teams which achieved second place at Defcon CTF 22 & 25. He has also presented at HITCON and PoC conferences. He is now focusing on Mobile and IoT security, particularly exploitation techniques.