(Reuters) -Steelmaker Nucor said on Wednesday it had halted certain production at various locations after identifying a cyber security incident that involved unauthorized third-party access to certain information technology systems it used.

The Charlotte, North Carolina-based company said it is in the process of restarting the affected operations as it investigates the incident along with external cyber security experts.

Nucor ( NUE ) has notified federal law enforcement authorities and is taking the potentially affected systems offline, while also implementing other containment, remediation or recovery measures, it said in an SEC filing.