The government's financial watchdog took administrative action Monday against Coincheck, the major cryptocurrency exchange hit last week by the largest theft of digital money on record.

The Financial Services Agency (FSA) said it issued a business improvement order for Coincheck's operations after NEM coins worth ¥58 billion — almost all of the customer assets it was holding — were stolen from the exchange Friday.

The costly hack underscored the security and regulatory difficulties surrounding bitcoin and other virtual currencies that are currently enjoying a global trading boom. The incident also came after the government made legal revisions in April to tighten Japanese regulations on cryptocurrency exchanges, amid surging interest in blockchain technology and following the collapse of bitcoin exchange Mt. Gox in 2014.