One of the world's biggest aluminium producers, Norway's Norsk Hydro, said Tuesday it had been hit by a cyber-attack of unknown origin.
"Our IT department is working to contain the impact" of the attack, he told AFP.
Most of the company's IT systems were affected, many of them disconnected and switched to manual operations.
The group's website was down on Tuesday morning.
The attack came a day after Hilde Merete Aasheim was appointed as the company's new CEO, replacing retiring Svein Richard Brandtzaeg. She became one of the few women to head a major global energy company.
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