In 2020, cyber-security researchers identified a hack in a piece of software called SolarWinds - which gave cyber-criminals access to 18,000 government and private computer networks. The hackers gained access to digital files of several US government agencies, including the treasury, justice and state departments.

Microsoft president Brad Smith said in February the SolarWinds hack was "the largest and most sophisticated" the world had ever seen.

The revelations of a major Russian cyber-campaign called Solar Winds last year caused dismay in Washington and raised difficult questions about how to respond.

Some in Congress likened it to an "act of war" and demanded retaliation. But others pointed out that the Russians had simply been engaged in exactly the kind of espionage that America itself also carries out online.

The US government has now announced sanctions targeted at 32 entities and individuals, including government and intelligence officials, and six Russian companies that provide support to the Russian government’s hacking operations. The U.S. is also expelling 10 Russian diplomats working in Washington, including some intelligence officers.

U.S. financial institutions are also barred from participating in the primary market for new debt issued by the Russian central bank, Finance Ministry and sovereign wealth fund. Those limits would take effect from June 14.

National Security Advisor Jake Sullivan told CNN earlier on Thursday April 15; 

“What President Biden is going to announce today, we believe, are proportionate measures to defend American interests in response to harmful Russian actions, including cyber intrusions and election interference. 

“His goal is to provide a significant and credible response but not to escalate the situation."

The sanctions are coming just two days after President Joe Biden warned President Vladimir Putin that the U.S. would defend its interests. He had also offered the possibility of a summit meeting in the coming months, drawing a cautiously positive response from Moscow.