Politico reported on Thursday that hackers targeted the Department of Energy (DOE) and its National Nuclear Security Administration (NNSA), which secures the US nuclear weapons stockpile.
The attack was part of a massive cyber campaign that affected at least half a dozen federal agencies, including the Treasury, State, Defense and Commerce Departments, Bloomberg reported.
The US has a total of 3,800 nuclear weapons, many of which were produced during the early years of the Cold War and are overseen by the NNSA.
US Secretary of State Mike Pompeo has suggested Moscow’s involvement but Russia has dismissed any such allegation as baseless.
US President-elect Joe Biden has described the cybersecurity breach as a matter of great concern, saying his team would impose “substantial costs” on parties responsible for such attacks.
Biden promised he "will make cybersecurity a top priority at every level of government, and we will make dealing with this breach a top priority from the moment we take office."