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Bithumb, South Korea's second-largest crypto exchange, said an unauthorized outside party had accessed its internal mobile groupware system, resulting in a leak of personal information, according to Yonhap News Agency.
The exchange is investigating whether customer data was compromised, Reuters reported, citing Yonhap. An industry source told Yonhap that some personal information belonging to Bithumb customers had been leaked.
Bithumb was one of three South Korean financial firms to report data breaches on Wednesday, local time. Brokerage Daishin Securities said the personal information of 38,490 customers, including names, email addresses and mobile phone numbers, was leaked after it detected signs of unauthorized access last week. It said it would compensate customers for any resulting damage in accordance with the law.
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Asset manager Mirae Asset Global Investments also confirmed a hacking incident, and financial authorities have begun an inspection.
Spokespeople for the three firms could not be immediately reached for comment by Reuters. The breaches follow a wave of hacking attacks on 16 South Korean financial firms, including banks, that had caused around 100,000 data leaks, the Financial Services Commission said earlier this month, according to Reuters.
The Korean breaches were reported the same day Coinbase said a security incident at analytics vendor Amplitude had exposed some of its customers' contact data. Binance founder Changpeng "CZ" Zhao listed all four incidents in a tweet on Wednesday, warning that leaked exchange data "is mostly used for phishing, SIM swapping, and social engineering."
"You can't prevent a leak, but you can protect yourself," Zhao wrote, urging users to sign up to each exchange with a unique email alias, avoid text message-based two-factor authentication and ask their phone carrier for a number lock. Leaked addresses and holdings data "have led to real-world extortion and robberies," he added.
Separately, South Korea's Science Ministry and the Korea Internet & Security Agency have urged website operators to check for recently disclosed flaws in PHP, the programming language behind much of the web, which let attackers run commands on a server without logging in. Bithumb has not said how its system was accessed.
The breach is the latest setback for Bithumb in 2026. In February, the exchange mistakenly credited 695 users with a total of 620,000 BTC, worth about $43 billion at the time, during a promotion meant to hand out small cash rewards. The deposits existed only on Bithumb's internal ledger, and the exchange said it recovered 99.7% of the Bitcoin.
In March, South Korea's Financial Intelligence Unit fined Bithumb 36.8 billion won ($24.6 million) and ordered a six-month partial suspension over anti-money laundering failures, but a Seoul court blocked the suspension in April.
Bithumb has since set out a three-stage plan to list on the stock market in 2028, while its CEO, Lee Jae-won, was booked as a bribery suspect in June over the alleged hiring of a National Assembly member's son.
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