Japan's Finance Ministry has admitted that sensitive government documents might have been leaked due to sophisticated Trojan malware that infected systems over the past two years.
A report by The Japan Times reports that the Trojan was discovered Tuesday by a company the Finance Ministry commissioned in May to check its computer security.
The Trojan malware reportedly infected 123 of 2,000 machines checked by the company.
Confessing that the attack had likely infected the government's network in January 2010, the government said that confidential information such as taxpayers' details had not been compromised.
According to the Finance Ministry, the last infection occurred in November 2011, after which it stopped. It also claimed that only data relating to ministry meetings had been leaked during the attacks, but did not provide any further details.
The report indicated that the government suspects hacktivist collective Anonymous is the culprit behind the attack due to the hacker group's recent increased interest in launching attacks against Japanese businesses to protest against a copyright infringement law passed by the government.
If that is the case, the Trojan would mark an escalation in Anonymous' attack pattern, as the collective's usual tactics typically have involved more basic techniques, such as distributed denial of service (DDoS) attacks.