At least eight viruses infected servers at Mitsubishi Heavy Industries, the company acknowledged Tuesday, with nuclear plant data believed to be among the targets of a coordinated cyberattack. MHI is a leading defense contractor in Japan and also provides a wide range of products and design services to the civilian nuclear industry. The viruses infected 45 servers and 38 individual computers and also put data on weapons systems at risk.International media quoted Japanese government officials as saying they are not aware of any sensitive information being accessed during the attack. Nonetheless, the government demanded that MHI conduct an investigation, which the company says will be complete by the end of the month.The attack occurred in August, MHI reported. It originated outside the company’s computer network and may have revealed some MHI information, like IP addresses.Nuclear plants and other security-sensitive institutions have become more focused on the risk of cyberattacks over the last decade. In the U.S., the Nuclear Regulatory Commission began requiring plants to address certain cyberthreats as they enhanced security after Sept. 11, 2001. By 2005, the NRC endorsed a program developed by the Nuclear Energy Institute to help licensees establish cybersecurity programs. That work now encompasses digital instrumentation and controls and a range of other plant safety applications. In 2009, the agency issued a new cybersecurity rule requiring all plants to submit their cybersecurity plans and timelines for NRC approval.