Hackers have broken into the networks of the US Treasury and Commerce departments just days after a leading global cybersecurity firm announced it had been breached in an attack that experts said bore the hallmarks of Russian tradecraft.

The FBI and the Department of Homeland Security’s cybersecurity arm are investigating what experts and former officials said appeared to be a large-scale penetration of US government agencies — apparently the same months-long cyberespionage campaign that also afflicted the prominent cybersecurity firm FireEye.

“This can turn into one of the most impactful espionage campaigns on record,” said cybersecurity expert Dmitri Alperovitch.

The hacks were revealed less than a week after FireEye disclosed that foreign government hackers had broken into its network and stolen the company’s own hacking tools.

Many experts suspect Russia is responsible. FireEye’s customers include federal, state and local governments and top global corporations.

The apparent conduit for the Treasury and Commerce Department hacks — and the FireEye compromise — is a hugely popular piece of server software called SolarWinds.

It is used by hundreds of thousands of organisations globally, including most Fortune 500 companies and multiple US federal agencies who will now be scrambling to patch up their networks, said Mr Alperovitch, the former chief technical officer of the cybersecurity firm CrowdStrike.

FireEye, without naming the breached agencies or other targets, said in a blog post that its investigation into the hack of its own network had identified “a global campaign” targeting governments and the private sector that, beginning in the spring, slipped malware into a SolarWinds software update.

The malware gave the hackers remote access to victims’ networks.

FireEye said it had notified “multiple organisations” globally where it saw indications of compromise.

The US government did not publicly identify Russia as the culprit behind the hacks, first reported by Reuters, and said little about who might be responsible.

Cybersecurity experts said last week that they considered Russian state hackers to be the main suspect.

National Security Council spokesman John Ullyot said in a statement that the government was “taking all necessary steps to identify and remedy any possible issues related to this situation”.

On its website, SolarWinds says it has 300,000 customers worldwide, including all five branches of the US military, the Pentagon, the State Department and the White House.

It says the 10 leading US telecommunications companies and top five US accounting firms are also among customers.

The government’s Cybersecurity and Infrastructure Security Agency said it was working with other agencies to help “identify and mitigate any potential compromises”.