Japan Parliament has been rocked after malware was found on three computers and a server possibly compromising usernames and passwords used access internal documents and emails.
Data from 480 Lower House members was reported by local media to have been compromised but investigators had not found evidence it was stolen.
The trojan has linked to command and control server was not yet thought to have been siphoned based in China, Ashai reported.
The infection lasted for a until August and began after a member had opened a malicious attachment sent by email.
Security software failed to prevent infection or stop the Trojan downloading "data stealing" software.
A Lower House committee held an meeting yesterday to investigate the incident.
Chief cabinet secretary Osamu Fujimura said the government would take "all possible measures" to improve security, Ashai reported.
Lower House members use the computers to email government agencies and other lawmakers. They also stored personal information including support groups, political accounting books and donations.
The attack comes on the heels of a malware infection that spread through machines owned by defence contractor Mitsubishi Heavy Industries last month.
The company detected up to eight different instances of malware including trojans and keyloggers in factories used to manufacture submarines, missiles and nuclear power plant components.