The agencies that maintain the U.S. nuclear weapons stockpile are reportedly preparing to notify Congress that they have evidence showing their systems were breached by foreign hackers in a monthslong cyberespionage campaign that came to light this week.

Officials from National Nuclear Security Administration and its parent agency, the Energy Department, were “coordinating notifications” about the breach, which they said also affected the Federal Energy Regulation Commission, to House and Senate energy and armed services committees on Thursday, according to Politico.