Aurubis, Europe's biggest copper smelter, said it had been the target of a cyberattack overnight that has forced it to shut down its IT systems and disconnect them from the internet.
"The IT systems are currently being examined," Aurubis said on Friday, adding that it was reviewing the scope of the impact.
Shares in Aurubis, which did not provide any further details, fell more than 4% on the news.
Germany's cybersecurity agency BSI warned earlier this week that cyber risks were the greatest they had ever been, with high levels of cyber crime and risks related to the war in Ukraine.
It said, however, that there did not appear to be any overarching attack campaign against German targets.
Earlier this year, a cyberattack on a satellite communications company knocked out remote control of thousands of wind turbines in central Europe.
Also, a German subsidiary of Russia's Rosneft was in March the target of a cyberattack by what BSI called "hacktivists" at Anonymous Germany. (Reporting by Maria Sheahan; editing by Matthias Williams)