U.S. Cybersecurity and Infrastructure Security Agency (CISA) has confirmed that Russian government-backed hackers stole emails from several U.S. federal agencies as a result of an ongoing cyberattack at Microsoft.

In a statement published Thursday, the U.S. cyber agency said the cyberattack, which Microsoft initially disclosed in January, allowed the hackers to steal federal government emails “through a successful compromise of Microsoft corporate email accounts.”

The hackers, which Microsoft calls “Midnight Blizzard,” also known as APT29, are widely believed to work for Russia’s Foreign Intelligence Service, or SVR.