Bank of China and Bank of East Asia have reportedly experienced hackings on their websites. The perpetrators later sent e-mails threatening more attacks unless the banks pay up, in bitcoins.

Both banks reported distributed denial of service (DDoS) attacks, affecting the performance of their websites. The banks said that customer service was not affected and that no sensitive data was compromised.

The Cyber Security and Technology Crime Bureau is investigating the attacks, which are believed to have originated from multiple countries.

Bank of China is one of China’s “Big 5” state-owned banks. Bank of East Asia is Hong Kong’s third largest bank. The Hong Kong Monetary Authority has requested that banks submit reports of the attacks.

Most of the 29 DDoS attacks reported to police last year targeted either government, public institutions or media websites.

The anonymous nature of bitcoin has made it a popular medium for extortionists looking to avoid apprehension by authorities. In most cases, victims have refused to cave into demands. However, victims have had no choice in some cases of ransomware attacks, where failure to comply can result in the loss of critical files.