A U.S. Department of Energy spokesperson said that on July 18 a Microsoft SharePoint zero-day vulnerability impacted its systems, including those of the National Nuclear Security Administration, which oversees the nation's nuclear weapons stockpile.

"The department was minimally impacted due to its widespread use of the Microsoft M365 cloud and very capable cybersecurity systems. A very small number of systems were impacted. All impacted systems are being restored," the department said in an emailed response to Reuters on Wednesday.