Vector Inc., a Softbank group firm that sells computer software online, said Thursday one of its servers was hacked into by an unidentified party and names and addresses of up to 261,161 customers might have been stolen.
The information that might have leaked out included that of credit cards. No abuse cases involving the massive leakage was known as of Thursday, according to Vector.
According to the company, the server detected the abnormality around 2:30 a.m. Wednesday.
Checking systems, Vector found traces of four unauthorized accesses from outside between 9 p.m. Tuesday and noon Wednesday.
Information on customers of computer software and online games is believed to have leaked out, the company said.
"We are sorry for causing trouble (to customers). We'd like to consider countermeasures by inviting experts," said Vector President Nobuhiro Kajinami during a news conference Thursday.
For inquires, call the firm (03) 5337-6712.