Nucor halts some production after unauthorized access to IT systems

Nucor, the largest US steel producer, disclosed on May 14, 2025 that it had identified unauthorized third-party access to some IT systems and had temporarily halted certain production operations as a precaution. Its filing gives no date for when the access was detected.

First filing

Nucor said it was restarting the affected operations and would continue to monitor materiality as its investigation went on.

June 2025 amendment

The 8-K/A said the threat actor had taken limited data. Production and the affected applications had been restored, and Nucor said it had brought back data from backups and believed the actor no longer had access. It concluded the incident was not material to its operations or finances.

Not specified

Nucor did not say which mills or locations stopped, for how long, or what data was taken.