Two of the largest Hong Kong banks were targeted with distributed denial of service (DDoS) attacks earlier this week by unknown parties demanding bitcoin ransoms.

Regional newspaper The Standard reported that the Bank of China (Hong Kong) and the Bank of East Asia were hit by the attacks last weekend. A representative for Bank of China confirmed that the attack took place on 9th May, telling CoinDesk:

“With our constant monitoring mechanism and contingency measures in place to ensure the security and operation of the Company’s website, our services and customer information have not been affected by the incident. The case was reported to the Hong Kong Police.”

The Bank of East Asia did not respond to requests for comment by press time.

A police spokesperson told The Standard that those behind the attack demanded payment in bitcoin following an initial DDoS attack, during which a website is flooded with significant amounts of fake traffic in order to disrupt access for other users.

The police spokesperson said the threats included promises of future attacks.

The reports come days after the extortion group DD4BC was blamed for a series of DDoS attacks against organizations in Switzerland, New Zealand and Australia, prompting a direct warning by a Swiss government agency.

DD4BC was cited as the source of a wave of attacks against some of the world’s largest bitcoin mining pools earlier this year, as well a variety of websites and services related to digital currency.