TOKYO — Computers in Japan’s Parliament have been found to be infected with a virus, officials said on Tuesday, the latest in a series of mysterious cyberattacks that have raised concerns about the leakage of sensitive information.

Personal computers used by three members of the lower house, as well as possibly a computer server, were infected by the virus, the top government spokesman, Chief Cabinet Secretary Osamu Fujimura, told reporters. He did not give details, but local media reports said the virus apparently had been used to hack into computers sometime in the past three months. The reports said log-in information and e-mails may have been stolen.

Media reports said one of the three lawmakers opened an e-mail attachment that released the virus.

The discovery comes a month after Japanese defense contractors revealed that they had also been targets of cyberattacks, which may have been aimed at classified military data. The contractors have said they did not know of any classified information being stolen.

Still, the reports raised concern in Washington since the contractors, which included Mitsubishi Heavy Industries, produce advanced American-designed weapons systems like the F-15 fighter jet. American security officials have already had doubts about Japan’s ability to handle sensitive information since a Japanese Navy officer was arrested in 2007 for leaking classified data on the American Navy’s advanced Aegis radar system.