In 2015, approximately 21 million people globally owned virtual currencies, but the I.R.S. estimates less than 900 people reported holding virtual currencies in U.S. tax returns. Now, the I.R.S. has adopted measures to ferret out crypto tax cheats. Whether modifying tax forms, cooperating with tax authorities through the J-5, or most recently stationing agents in international financial centers, the I.R.S. is serious in its attempts to track and tax cryptocurrency transactions. In their article, Stanley C. Ruchelman and Lisa Singh, an extern at Ruchelman P.L.L.C. and a student at New York Law School, look at recent global efforts.