The Office of Foreign Assets Control (OFAC), a watchdog agency tasked with preventing sanctions violations, on Monday added Tornado Cash to its Specially Designated Nationals list, a running tally of blacklisted people, entities and cryptocurrency addresses. Tornado Cash has been a key tool for the Lazarus Group, a North Korean hacking group tied to the $625 million March hack of Axie Infinity’s Ronin Network, according to the Treasury Department.