A Japanese power plant worker has inadvertently leaked nuclear secrets onto the web thanks to a virus infection.

The unnamed employee had stored about 40MB of confidential reports on his home PC. When the system was infected with a virus the details were leaked.

The data is said to have been distributed to users of the Winny peer-to-peer system, the most popular file-sharing network in Japan.

"If you allow your employees to put sensitive company data onto their home computers, you are running the risk that they will not be as well defended as the PCs within your organisation," said Graham Cluley, senior technology consultant at Sophos.

"Security at power plants should be at an all-time high, but it needs to extend beyond the physicality of barbed wire and high walls and encompass information security too."

Sites referred to in the leaked data include Kansai Electric Power's Mihama nuclear plant and a power station in Tsuruga, as well as pressurised water reactors in Tomari and Sendai.

Authorities have been quick to reassure the public that it does not believe the information leaked was directly related to radioactive substances.