More than 300 files of information, including those related to transportation security, may have leaked out after a personal computer at Hokkaido Railway Co. came under cyberattacks, NHK reported on Monday.

The company, known as JR Hokkaido, was targeted by cyberattacks when it was preparing for the opening of the Hokkaido Shinkansen Line scheduled for next month.

In August, a company official opened a file attached to an email that appeared to come from a customer making an inquiry. As a result, as many as seven personal computers were infected by a virus, the report said.

The company's investigation found signs that someone remote-controlled the infected office personal computers and tried to steal more than 300 files in the company's system. The files include information related to the railway's security and measures to protect transportation services from crimes. The report said such information may have been leaked to the outside.

JR Hokkaido is planning to introduce a new system that prevents emails from a third party from directly reaching its employees and revise its overall security measures, the report said.

In recent years, JR Hokkaido has often been accused of safety oversights. The carrier has been struggling to regain public trust after scandals over shoddy track maintenance records and data manipulation.