James Zhong appeared to have pulled off the perfect crime. In December 2012, he stumbled upon a software bug while withdrawing money from his account on Silk Road, an online marketplace used to hide criminal dealings behind the seemingly bulletproof anonymity of blockchain transactions and the dark web. Mr. Zhong, a 22-year-old University of Georgia computer-science student at the time, used the site to buy cocaine. “I accidentally double-clicked the withdraw button and was shocked to discover that it resulted in allowing me to withdraw double the amount of bitcoin I had deposited,” he later said in federal court. After the first fraudulent withdrawal, Mr. Zhong created new accounts and with a few hours of work stole 50,000 bitcoins worth around $600,000, court papers from federal prosecutors show. Federal officials closed Silk Road a year later on criminal grounds and seized computers that held its transaction records. The records didn’t reveal Mr. Zhong’s caper at first. Authorities hadn’t yet mastered how to track people and groups hidden behind blockchain wallet addresses, the series of letters and numbers used to anonymously send and receive cryptocurrency. One elemental feature of the system was the privacy it gave users.

Full report  : The U.S. Cracked a $3.4 Billion Crypto Heist—And Bitcoin’s Anonymity.