A British nuclear power station suffering an "unplanned outage" has categorically denied any link to the sophisticated Stuxnet worm.
One of two reactors at Heysham 1, owned by French energy giant EDF, was taken offline yesterday.
Parts of the site are run by Siemens S7 systems, prompting suggestions the sophisticated worm is to blame for the shutdown.
An EDF spokeswoman told The Register the suggestions amounted to "conspiracy theories".
"I can confirm that on Heysham 1 there is no Siemens S7 equipment in any safety-related applications," she said.
"There is absolutely no link between the cause of Heysham 1's trip yesterday and any 'cyber security' issues".
EDF declined to give a detailed technical explanation for the ongoing outage, citing regulations that forbid the release of such information. The regulations are designed to prevent distortion of the energy market based on speculation over when electricity production may resume.
Security researchers discovered earlier this year that Stuxnet exploits vulnerabilities in the type of Siemens control system used at Heysham, and in Microsoft Windows.
The sophistication of the attack - the EU information security agency ENISA called it "a new class and dimension of malware" - led many to believe it had been created by a state intelligence agency, possibly to disrupt Iran's civilian and military nuclear programme. Siemens and Microsoft have since released patches to secure their software.
To date there is no evidence that Stuxnet has affected any British facilities. ®