Japanese government officials have denied reports that a secure network used by the country's defense forces was attacked earlier this year.
An attacker was able to break into the Ground Self-Defense Force's computer systems, sources at the Japanese Ministry of Defense told Kyodo News on Sunday. The ministry and the Self-Defense Forces discovered the attack in September, said the report, which was also relayed by The Japan Times.
Kyodo's sources said the hack was believed to be the work of a nation state, and that information may have been leaked in the attack.
But on Monday, a ministry representative told Bloomberg News that Kyodo's report was untrue.
The ministry receives numerous suspicious emails and other contacts believed to be cyber attacks each day, but the ministry won't comment further because to do so could reveal its defenses, the representative told Bloomberg.
The alleged September attack, though, didn't involve e-mail. Rather, the attacker was able to use computers at the National Defense Academy and the National Defense Medical College as a gateway into the Defense Information Infrastructure, which connects Self-Defense Force bases.
The Defense Information Infrastructure consists of two networks, one open and one closed. The open network is connected to the internet via a firewall, according to the ministry's website. The hacker used a link between the two to conduct the attack, Kyodo's sources said.
The government immediately raised its cybersecurity alert level upon discovering the attack, and temporarily banned ministry and Self-Defense Force staff from accessing the internet, Kyodo said.
It's only three years since Japan created its own Cyber Defense Unit, reporting to the ministry through the Command Control Communication Computers Systems Command (C4SC), to strengthen its computer systems against cyber attacks.