The payment system of ONUS, the largest cryptocurrency trading platform in Vietnam, running a vulnerable version of Log4j suffered a cyber attack. Cyclos notified ONUS to repair the system on December 13, but it was too late. Although ONUS has fixed the security loopholes in the Cyclos instance, the window of loopholes allowed attackers to successfully steal data from sensitive databases. The stolen database contained nearly 2 million user data, including KYC (Know Your Customer) data, hashed passwords, etc. Subsequently, the attacker asked ONUS to pay a ransom of 5 million, otherwise the stolen data would be made public. On December 25, because ONUS did not pay the full ransom, the attackers sold customer data on the dark web data exchange market.