Norfolk Southern has finished a root cause analysis into what caused Monday’s temporary system outage and says the incident appears to be related to a vendor software defect.

The railroad said hacking wasn’t a factor, according to a Friday update. “To date, we have found no indication that this was related to an unauthorized cybersecurity incident.”

Rather, there was a defect in the software that handles NS’ (NYSE: NSC) data storage system, which is manufactured and maintained by a global technology provider, the company said. That defect created an error that caused NS’ primary and recovery data systems to become unresponsive, NS said, which subsequently affected core operational systems.

The outage impacted the rail operations of not only NS but also commuter and passenger rail service. Amtrak said Tuesday that the technology hardware issues caused delays and cancellations for some Amtrak trains in the Midwest and Mid-Atlantic.

NS is working with the vendor to see how to prevent this from happening again.

“Throughout this, our IT team worked tirelessly to restore our systems, our Marketing team worked closely with customers to keep them informed, and our Operations team safely brought our network back online,” NS said. “We are making progress on the temporary backlog of trains that resulted from this incident, and expect a full recovery of network fluidity in the coming weeks.”

Subscribe to FreightWaves’ e-newsletters and get the latest insights on freight right in your inbox.

Click here for more FreightWaves articles by Joanna Marsh.

Related links: