After the country’s largest underground banking operation was dismantled by authorities in China last week, handling online gambling transactions in the country could become much more difficult.

Approximately 100 suspects were detained by police in Zhejiang province on China’s eastern coast in connection with an illegal banking system, according to an announcement on Thursday by the Ministry of Public Security. In what authorities are calling the largest “grey capital” bust in China’s history, transactions totaling US$64.2b were handled, according to local sources.

The bust is the result of a month-long crackdown on illegal foreign-exchange transactions, which according to officials disrupt the country’s financial management, help criminals and terrorists launder money and facilitate corruption. It was reported that the suspects comprised a network of eight gangs that worked out of more than two dozen “criminal dens” routing money through hundreds of accounts held in China and Hong Kong financial institutions to avoid restrictions on moving currency outside of China.

Warrants were issued three months after Chinese authorities began their investigation of the ring in September 2014. All of the affiliated companies that handled over a million transactions through 850 different bank accounts had to be sorted through, which account for the lengthy period of time. Via CalvinAyre, according to the Xinhua news agency, one of the gang leaders said his group earned as much as US$7,830 a day per the set-up. It is believed that operations similar in nature charge up to a 5% fee of the transferred sum, depending on the individual transaction size.

In an attempt to shore up the local currency and reduce corruption, in August China announced it was putting the clamps down on illegal banking operations, which would be accomplished by preventing the illegal conversion of yuan to dollars. The crackdown on underground banks is one way the country is attempting to reduce corruption among public officials, which is commonly cited as a major contributor to the year-and-a-half long revenue decline at Macau casinos.

Not the first major illegal gambling bust in China this year, more than 7,500 properties, including gambling venues and residences, in Hong Kong were raided over a three-month period by Hong Kong police earlier this year. Those raids resulted in the arrests of approximately 4,343 people with alleged ties to the city’s infamous organized crime syndicate, the triads, suspected of organized-crime activities in Hong Kong, Macau and the Guangdong province.