U.S. Homeland Security staff were unable to access DHS computer network because the security certificates expired

Some employees with the U.S. Department of Homeland Security who work in the Washington, D.C. area and in Philadelphia, PA were unable to access the DHS computer network on Tuesday, reports Reuters, citing "three sources familiar with the matter."

No word on exactly how widespread the problem was, or how it impacted DHS. The agency has been a focus of Donald Trump's recent speeches, and its domain includes immigration, border security, and "cyber defense."

The cause? Expired security certificates.

"We are working to track all device certificate issuance and expirations to ensure future lapses of service do not occur," a DHS official said.

Snip from Reuters:

In a statement, a DHS official confirmed a network outage that temporarily affected four U.S. Citizenship and Immigration Services (USCIS) facilities in the Washington area due to an "expired DHS certificate."

Reuters first reported the incident earlier Tuesday, which a source familiar with the matter said also affected a USCIS facility in Philadelphia.

Employees began experiencing problems logging into networks Tuesday morning due to a problem related to domain controllers, or servers that process authentication requests, which could not validate personal identity verification (PIV) cards used by federal workers and contractors to access certain information systems, according to the source.

Some employees were able to access systems through a virtual private network. It was not clear if other branches of DHS were affected.

The source characterized the issue as one stemming from relatively benign information technology missteps and a failure to ensure network redundancy. There was no evidence of foul play, the source said, adding that it appeared the domain controller credentials had expired on Monday when offices were closed for the federal Presidents Day holiday.

PHOTO: A U.S. Customs and Border Protection agent applauds President Donald Trump's remarks at Homeland Security headquarters in Washington, U.S. January 25, 2017. REUTERS/Jonathan Ernst