A string of hacks of U.S federal agencies and corporations identified last month "likely" originated in Russia, the U.S. Director of National intelligence said on Tuesday.
A joint statement issued by federal security agencies said the hackers' goal appeared to be collecting intelligence, rather than any destructive acts.
They said they had identified 'fewer than 10' agencies that were hacked, although added that the investigation is ongoing and more government victims may be identified.
The statement is the first concrete attribution of the incident by the Trump administration.
Meanwhile, Russian officials have denied involvement and did not immediately respond to questions.
Security company FireEye - which was itself breached - discovered the new round of hacks, many which were later traced to a tainted software update from the network-management developer, SolarWinds.
As many as 18,000 customers downloaded the updates at companies like Microsoft and U.S. federal departments including Defense, State, Treasury and Homeland Security.
The breach is considered the worst known cyber-compromise in the last five years.
Previously, President Donald Trump suggested the hackers could be from China, but Secretary of State Mike Pompeo quickly said in a radio interview that it was quote 'pretty clear that it was the Russians that engaged in this activity.'
Meanwhile, President-elect Joe Biden criticized the President's response and has promised an 'overwhelming focus' on the hacks when he assumes office in January.