TOKYO - A hacker believed to be behind an unauthorized intrusion affecting a foreign exchange trading service of Japanese internet service provider GMO Internet Group Inc. disclosed some customer information Tuesday after threatening to do so, cybersecurity sources said.
A statement from the hacker claimed information linked to GMO customers had been posted online after the company failed to respond to a ransom request, the sources said.
Asked about the statement and the alleged disclosure of customer information, GMO said it "refrains from commenting on every event."
GMO said late Monday that the hacker had threatened to disclose customer information and conduct a ransomware attack at noon. Prior to noon, GMO had called on users to back up data and unplug their computers.
From Monday, GMO began analyzing the devices of customers who have agreed to cooperate with its investigation. The move is intended to assess the extent of the unauthorized access, including whether malware has actually been installed.
The company will notify service users individually by email once countermeasures are identified.
The unauthorized access targeted the Onamae.com Desktop Cloud service. An investigation following a customer inquiry confirmed on Oct. 20 that an unauthorized program had been installed by a third party in the server environments of some customers.
GMO CEO Masatoshi Kumagai said Monday in a blog post that the hacker was demanding $50 million in cryptocurrency, which he said the firm will not pay.
In a press release issued the same day, the company reiterated that it will not comply with the attacker's demands, given that deletion of the information and prevention of its misuse cannot be guaranteed.
Finance Minister Satsuki Katayama, meanwhile, said that the government is urging financial institutions to take measures to defend against potential cyberattacks, noting that five foreign exchange trading firms using the GMO server service, such as OANDA Japan Inc., had been affected.
The companies, including Goldenway Japan Co. and Ava Trade Japan K.K., have reported to the Financial Services Agency that customers had been affected by the GMO cyberattack.
"We cannot rule out the possibility of further unauthorized transactions, so we will respond with a sense of urgency," said Katayama, who also serves as financial services minister.
