US Steel Producer Nucor Corporation faces operational disruptions after cyberattack

Nucor Corporation, the largest steel producer in the United States, is reporting operational disruptions following a cybersecurity incident involving unauthorized third-party access to its information technology systems. The company serves as a primary supplier of reinforcing bar that is extensively used in the nation's buildings, bridges, roads, and other critical infrastructure projects.

After detecting the breach, the company took affected systems offline. The attack has had considerable operational impact, forcing Nucor to temporarily suspend production at multiple facilities. The extent of the business disruption is not clear. 

The nature and scope of the cyberattack is not disclosed. The company has not provided details about the date when the incident occurred, any exposed data or individuals, or whether the unauthorized access resulted in data theft or system encryption. No ransomware groups have publicly claimed responsibility for the attack at the time of reporting, leaving the identity of the perpetrators unknown.

In 2023, Nucor was hit by a cyberattack exploiting an unpatched software vulnerability.

The company has notified appropriate law enforcement authorities about the breach and has engaged external cybersecurity experts to assist with the ongoing investigation. Nucor reports they are in the process of gradually restarting operations. 

Update - as of 23rd of June 2025, Nucor reports that the attackers stole data from the company's network. "The Company's investigation also determined that the threat actor exfiltrated limited data from the Company's information technology systems. The Company is reviewing and evaluating the impacted data and will carry out any appropriate notifications to potentially affected parties and to regulatory agencies as required by applicable law."

Nucor has not disclosed the exposed data typesor number of affected individuals.