"The ministry will continue to monitor the problem and conduct investigations if necessary," Ichikawa added.
The company, which makes warships, submarines and other defence-related equipment, said on Sunday that 45 Japan-based servers and 38 computer terminals were infected with viruses during a cyber attack in mid-August.
The machine that attackers used to remotely operate the affected computers appeared to be displaying Chinese language script, the Yomiuri daily reported in its Tuesday evening edition, citing unnamed sources.
Beijing shrugged off suggestions that it was behind the crime, with foreign ministry spokesman Hong Lei saying: "Such allegations are groundless."
"The Chinese government is willing to co-operate with other countries to fight against cyber crimes including hacking," he said.
Another Japanese defence contractor and heavy industry firm IHI said it had also come under attack, receiving an increasing number of emails carrying virus-laden attachments over the last few months.
"We have been able to prevent any real damage and infection. We are checking the health of our IT system just as precaution," an IHI spokesman said.
IT security firm Trend Micro said it had uncovered a campaign of targeted attacks that have successfully compromised defence industry companies in Japan, Israel, India and the United States.
"We have been able to identify eight victims of this attack and are in the process of notifying them," the company said in a blog dated Monday.