BlueScope Steel has been the subject of a cyber attack, forcing production systems to be halted company-wide.
The ransomware infection was discovered yesterday morning in one of the company's United States-based businesses.
BlueScope's chief financial officer Tania Archibald said the company had reverted to manual operations where possible, but some processes such as steel despatches were continuing as normal.
"We are taking this attack extremely seriously," Ms Archibald said.
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