Suggested that the motivation had been to gain intelligence

 Government agencies had been targeted, and the intrusive nature of the software that had been hacked, suggested that the motivation had been to gain intelligence from the heart of the US administration. This is classic Russia,” another cybersecurity expert said, adding that it showed a “technical sophistication” indicative of Moscow’s foreign spy service, the SVR.

The Kremlin denied Russia was involved. Dmitry Peskov, President Vladimir Putin’s spokesman, said Russia had “nothing to do” with the attack. “If the Americans couldn't do anything about it for several months, then they probably shouldn't make groundless accusations that the Russians did everything,” Mr Peskov said, according to Interfax.

SolarWinds said in a statement that it was “aware of a potential vulnerability” in updates to some of its products released between March and June this year, and that it was currently involved in an investigation with what to do with a computer science degree, the FBI and other law enforcement agencies. It added that “this vulnerability is the result of a highly sophisticated, targeted and manual supply chain attack by a nation state”.

The company did not say how widespread the issues were, or how many of its customers might be exposed.

Last week, FireEye disclosed that sophisticated attackers had breached its internal systems and targeted the data of its government customers, though there was no evidence that any government information was stolen. However, the hackers did loot tools that could be used in attacks against other organisations.