NASHVILLE, Tenn. (AP) — A federal investigation into how guards at a Tennessee nuclear weapons plant got copies of questions in advance of a written security skills test has called on the Department of Energy to improve its oversight of private contractors.

DOE inspector general Gregory H. Friedman said in a report Wednesday the questions were widely distributed among security officers at the Y-12 plant in Oak Ridge. Similar compromises may have occurred at other DOE sites and not been discovered, the report concluded.