Institutions are in the government, voluntary and consulting sectors.
The hackers targeted organizations working mainly in the areas of human development and human rights. Although most of the attacks are in the US, e-mails have been sent to individuals in 24 countries, said Tom Burt, vice president of Microsoft. It is not clear which countries these are.
The message said that the then US President Donald Trump had published the documents of the fraudulent activities to overthrow the last election and instructed to click on the link to read them. If the user clicks on the links in the mail, the virus will invade the user's computer system and lead to further cyber attacks, data theft and other activities.
The latest attack comes less than a month after the US imposed sanctions on Russia over a series of cyber-attempts and hacking attempts at solar winds in the US presidential election.
US aid sources confirmed the attack and said a cyber forensic investigation into the incident was underway. Microsoft has said it has been working on the attack since the beginning of this year, and confirmed that the mass mailing took place on Tuesday.
But White House circles have taken the approach of downplaying the incident.
White House sources said U.S. agencies have resisted and neutralized the cyber-attack. They said most of the emails were likely to go to the spam category and that a significant number of US companies had not been hit by a cyber attack.
But the US's soft approach is seen as diplomatic.
The summit is scheduled for June 16 between US President Joe Biden and Russian President Vladimir Putin. Before the meeting that the world is looking at, the intention is not to stonewall such an event. It is also noteworthy that the US did not criticize Russia in the incident. Russia's foreign intelligence service has denied the allegations in a statement issued Friday stating "Similar, baseless allegations concerning Russia's intelligence have been made more than once.
