One of the world's biggest aluminium producers, Norway's Norsk Hydro, on Tuesday said it had been hit by a cyber-attack of unknown origin.
"Hydro became victim of an extensive cyberattack in the early hours of Tuesday, impacting operations in several of the company's business areas," the energy group said in a statement.
Spokesman Halvor Molland said it was too early to determine the full extent of the attack, or its 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 news sent the firm's share price tumbling 2.0 per cent in early trading on the Oslo Stock Exchange.
Norway's National Security Authority (NSM), tasked with protecting the country from cyber attacks, espionage, sabotage or acts of terrorism, said it was assisting Norsk Hydro.
"We are obviously trying to identify whether it will spread, but we have not detected anything yet," NSM's communications director Mona Strom Arnoy said.
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.