Cyber attackers attempted to break into America’s Fermi National Accelerator Laboratory using a security hole in Microsoft’s SharePoint software, the Department of Energy confirmed today.

The hackers targeted the particle physics lab’s SharePoint servers after exploiting a vulnerability first discovered in May. Microsoft released a fix last month, but security experts say the patch didn’t fully seal the gap. FermiLab – home to advanced particle accelerators – quickly detected the intrusion. "Impact was very limited," a DOE spokesperson stated. "No sensitive or classified materials were accessed."

This marks the second confirmed SharePoint-related breach at U.S. energy facilities this month. On July 18. the same flaw affected Department of Energy systems including the National Nuclear Security Administration, which manages America’s nuclear weapons stockpile. Officials stress no nuclear secrets were compromised.

FermiLab’s systems are now back online. Microsoft hasn’t commented on why its June security update failed to completely resolve the issue. The vulnerability has reportedly enabled global espionage operations since spring.

The Illinois-based lab, established in 1967. studies subatomic particles using massive underground accelerators. Like other DOE facilities, it handles non-military research data. The department maintains all affected systems are "operating normally" following the incidents.