In January 2018, more than half a billion dollars' worth of a cryptocurrency was siphoned from a major exchange in Japan. The thief deftly evaded detection, and efforts to uncover the truth seemed to lead to a dead end. But a group of IT specialists called white hat hackers didn't give up. One wrote a program designed to close in on the culprit. Another teamed up with engineers around the world to uncover the thief's identity. We followed the battle between the white hat hackers and the perpetrator for 3 months.