Police in China’s northern city of Xi’an have recently arrested three suspects for allegedly stealing up to 600 million yuan ($87 million) worth of cryptocurrencies by hacking, Huashang News reported on Saturday. This is the largest-ever cryptocurrency heist in the country.

The police started investigating the case on March 30 when a man from the city complained that hackers had invaded his personal computer to loot more than 100 million yuan worth of bitcoin and ether.

An initial investigation revealed that the suspects with advanced hacking techniques had remotely hacked the virtual currency account and left few traces behind. And the anonymous trading of cryptos also added the complexity to the case.

Investigators said hackers had split the amount of stolen digital assets into smaller units and conducted multiple transactions in order to cover their tracks. Police analyzed roughly 30,000 pieces of information and approached the assistance from domestic internet. A three-month effort led to identify the first suspect named Zhou in the central province of Hunan.

And it took another 2 months before they arrest the other two accomplices: a man surnamed Cui in Beijing and Zhang in Jilin province.

According to police, all the three suspects are veteran hackers who once worked for top internet firms. The gang has amassed 600 million yuan worth of cryptocurrencies by hacking the PCs of people and organizations. And they sold part of the stolen digital assets to buy high-end villas, cars and wealth management products.

Further investigation is underway.

As the blockchain hype train has been operating at full steam, blockchain security issues have led to an economic loss of over $2.7 billion in the first half of 2018, according to the recent report from Tencent, a tech giant in China.Aiming to fight blockchain-related security issues in China,  Tencent’s security arm, CTMA, together with the China Blockchain Application Research Center and 20 other public and private institutions, launched the government-backed blockchain security alliance in late June.