The US energy department is the latest agency to confirm it has been breached in what is being described as the worst-ever hack on the US government.
The department is responsible for managing US nuclear weapons, but said the arsenal's security had not been compromised.Tech giant Microsoft also said on Thursday that it had found malicious software in its systems.
Many suspect the Russian government is responsible. It has denied any role.
The US treasury and commerce departments are among the other targets of the sophisticated, months-long breach, which was first acknowledged by officials on Sunday, BBC reported.