The attack on SolarWinds software users that the U.S. accuses Russia of was the worst cyber espionage attack on the U.S. government in history.
According to the agency, 27 U.S. attorneys had at least one office computer hacked.
This raised fears that hackers may have gained access to sensitive information, including the names of informants.
Prosecutors’ emails contain highly sensitive, highly confidential and often highly classified information.
If hackers learned the names of confidential informants, they could use that information to “blow their cover.”
The hack, which gave cybercriminals potential access to 18,000 government and private computer networks, was made public last December.
Among those affected by the hack are 80 percent of the Microsoft e-mail accounts used by employees of four New York City prosecutors’ offices, which are pursuing some of the most high-profile lawsuits in the country.
They include many high-profile financial investigations, which means that any leaked information could be used for blackmail or extortion.
In April, U.S. President Joe Biden’s administration announced sanctions against Russia in response to the SolarWinds hack and other cyberattacks.
Russia as always denies any wrongdoing.