Washington – The unclassified email network used by Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, and hundreds of military and civilian personnel was taken offline over the weekend after suspicious activity was detected, the Pentagon confirmed to CNN on Tuesday.

Officials will not say exactly what happened, but the U.S. military’s Cyber Command is now investigating the matter according to Lt. Col. Valerie Henderson, a Pentagon spokesman.

So far, there is no indication any classified systems were impacted, officials say.

Dempsey and other critical senior personnel have been provided “a work around” so they can access their unclassified email, a defense official said.

Right now the focus is on “mitigating the cyber security risks we see across our impacted network,” the official said.

As reported by CNN