BOSTON, June 10 (Reuters) - A suspected Russian hacker is

now in U.S. custody following his arrest in Thailand last year

and has been charged with facilitating a campaign of

cyberattacks carried out by a Russia-aligned group that

victimized numerous U.S. companies.

Denis Obrezko, 36, made his initial appearance in federal

court in Boston on Tuesday in connection with a case that U.S.

authorities alleged concerned a large-scale cyber espionage

campaign being carried out by a group known as Void Blizzard.

He was charged with conspiring to commit unauthorized access

to a protected computer and is now being held without bond in a

case that is being prosecuted by the U.S. Department of

Justice's National Security Division.

The U.S. Justice Department and a court-appointed lawyer for

Obrezko did not immediately respond to requests for comment on

Wednesday.

Void Blizzard had been flagged by Microsoft ( MSFT ) in a

May 2025 report as what it said was a new group that it had

observed conducting cyber espionage activity against

organizations important to Russian government objectives.

Active since at least April 2024, Void Blizzard's activity

has primarily targeted organizations in NATO member states and

Ukraine across multiple sectors, including government, defense,

transportation, media, healthcare and non-governmental

organizations, Microsoft ( MSFT ) said.

An FBI agent in an affidavit filed in connection with the case

against Obrezko said Void Blizzard's activity has focused

primarily on mass email harvesting across a wide range of U.S.

business sectors and industries.

The FBI has identified at least 11 U.S. companies that have

been hacked, a number that is believed to be just a fraction of

Void Blizzard's victims, the court filing said.

According to charging documents, the FBI linked Obrezko to

cryptocurrency transactions that were carried out to buy a

virtual private server and domain name that were used to conduct

attacks targeting companies in the United States and elsewhere.