Nikkei news agency said some of its subscribers' personal information might have been leaked on 1,644 occasions, raising eyebrows over its data security.
It said the incident has been reported to the privacy commissioner in Hong Kong.
This came as unauthorized access to some e-mail accounts used by Nikkei China (Hong Kong) - an overseas group company - and Nikkei's Hong Kong bureau had been detected since October.
Nikkei said overseas subscribers to its international edition, web edition and Nikkei Asia under contracts with Nikkei China saw their names, e-mail addresses, company names, addresses and phone numbers exposed to the risk of leakage.
The news agency said this also included 24 occasions of possible leaks of credit card details belonging to corporate subscribers and information of senders of news releases to its Hong Kong bureau.
But the news agency said its Japanese subscribers had a narrow escape over the leaks.
"We apologize for the trouble and worry we have caused many people," a spokesman said."We will tighten our control of personal information and work to prevent similar occurrences."
The Office of the Privacy Commissioner for Personal Data confirmed yesterday that it had received a report from Nikkei Wednesday.
The office said it would conduct a compliance check to find out details from the news agency, including whether any Hong Kong customers were affected and if so the number involved.
Privacy commissioner Ada Chung Lai-ling reminded organizations to take effective security measures in order to protect customers' personal data.
"The privacy commissioner appeals to organizations to notify the PCPD and the affected customers as soon as possible of any data breach incidents to minimize the potential damage which might be caused to customers," Chung said.