As many as 440,000 items of personal data, including more than 300,000 linked to the Line messaging app, have been leaked, Japanese tech giant LY said Monday, due to unauthorized access of an affiliate's computer system in October.
There have been no reports of misuse so far, the company said.
It said the leaked data included users' age groups, genders, and some of their service use histories, as well as information regarding the company's business partners and employees, such as email addresses, names and affiliations.
While the company confirmed the data leak on Oct. 29, it said it took about a month to make the announcement, as it required time to confirm the scale of the breach.
"We sincerely apologize to our users and all relevant parties for any inconvenience or concern caused. We deeply regret this incident and will do our best to prevent any reoccurrence," the company said in a statement.
It has reported the case to the communications ministry.
LY was formed in October through the merger of Z Holdings and its group companies Yahoo Japan, a news portal site operator, and Line.
The leakage was caused when malware infected a computer owned by an employee of a subcontractor used by the company's South Korea-based affiliate Naver Cloud, it said.
Naver Cloud and LY share an in-house system for dealing with employee and other personnel information that is managed with a common authentication system, and this allowed unauthorized access into LY's internal system, the company said.
It said it is contacting users, business partners and customers individually who it believes are at risk of damage due to the leakage.