Key facts
- Denis Obrezko, a suspected Russian hacker, has been charged in U.S. federal court in Boston.
- Obrezko was arrested in Thailand and brought to the U.S.
- He is accused of facilitating cyberattacks by a Russia-aligned group called Void Blizzard.
- Void Blizzard has targeted organizations in NATO member states and Ukraine, including at least 11 U.S. companies.
- The group's activities include mass email harvesting and cyber espionage.
- Obrezko allegedly used cryptocurrency to purchase virtual private servers and domain names for the attacks.
A suspected Russian hacker, Denis Obrezko, 36, has been charged in U.S. federal court in Boston with facilitating a campaign of cyberattacks. Obrezko was arrested in Thailand last year and is now in U.S. custody.
Authorities allege Obrezko aided a Russia-aligned group known as Void Blizzard, which has been conducting cyber espionage and unauthorized access to protected computers. Microsoft flagged Void Blizzard in a May 2025 report as a new group observed conducting cyber espionage against organizations important to Russian government objectives.
Void Blizzard has been active since at least April 2024, primarily targeting organizations in NATO member states and Ukraine across various sectors, including government, defense, transportation, media, healthcare, and non-governmental organizations. The FBI stated that Void Blizzard's activities have focused on mass email harvesting across a wide range of U.S. business sectors, identifying at least 11 U.S. companies that have been hacked, though this number is believed to be a fraction of the total victims.
Charging documents indicate that the FBI linked Obrezko to cryptocurrency transactions used to purchase a virtual private server and domain name that were employed in attacks targeting companies in the United States and elsewhere. Obrezko made his initial appearance in court on Tuesday and is being held without bond.