Information related to communication networks involving Japan's Self-Defense Forces may have leaked after cyberattacks were conducted earlier this month against NTT Communications Corp., a source familiar with the case said Thursday.
The Defense Ministry is investigating the case in cooperation with the company, an affiliate of Nippon Telegraph and Telecom Corp., suspecting that the possible leaks could affect operations of the SDF's core system, the source said.
The suspected leaks involve information about communications equipment and layout of a Maritime Self-Defense Force facility in Yokosuka, south of Tokyo, as well as that of communication lines in about 10 SDF locations.
More than 100 data files were accessed without authorization, according to the source.
All the data were linked to business that NTT Communications had received from the ministry.
The data do not appear to be "secrets" as designated by the ministry, but there is concern the leaked information may undermine a communications network between the ministry and the SDF.
On Thursday, NTT Communications said information regarding 621 client companies may have leaked because of unauthorized access to its network.
It declined to release the names of the companies, citing the need to keep their privacy.
NTT Communications said it would reserve commenting on whether defense-related information could have been leaked.
According to the source, the company shut communications with the outside after detecting abnormal activities against its servers on May 7.
By May 13, investigations found that there were possible leaks.
The company found multiple unauthorized accesses to Defense Ministry-related information from May 4 to 5 through a Singapore-based server.
NTT Communications reported the case to the ministry on May 13 but said it saw no fear of possible leaks of secrets and information that must be protected, the source said.
The case is the latest in a series of cyberattacks on Japanese defense-related companies such as Mitsubishi Electric Corp., NEC Corp., and Kobe Steel Ltd.
An attack on Mitsubishi Electric in January may have provided hackers with data regarding the capability of a cutting-edge high speed gliding missile.