On May 9, an international group of hackers launched distributed denial of service (DDoS) attacks on two of the largest financial institutions in Hong Kong.

Hong Kong police confirmed that they have received reports from the Bank of China and the Bank of East Asia claiming that the hackers demanded payments in bitcoin.

"The two institutions later received emails demanding payments in bitcoins, or there would be another round of attacks," a spokesman said.

According to The Standard Hong Kong, the hackers overwhelmed the websites of the two banks with traffic from multiple sources, causing irregular spikes in Internet traffic and forcing some of the websites' resources to be unavailable.

However, both banks stressed that none of its data and customer accounts were compromised.

Finance Magnets reported that the Cyber Security and Technology Crime Bureau has classified the case as "blackmail" and has begun an investigation.

The attack imposed on the two banks is similar to the DDoS attacks launched on the official corporate websites of banks in China and Hong Kong, most notably the People's Bank of China in late 2013. The investigators at the time believed that the attacks were a result of the issuance of new rules which prohibited financial institutions from dealing with bitcoin.