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

U.S. custody after being extradited from Thailand 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, who was arrested in Thailand in November,

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.

The 36-year-old 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 Justice Department had no comment on Wednesday, and a

court-appointed lawyer for Obrezko did not respond to a request

for comment.

Thailand's Ministry of Foreign Affairs said in a statement

the Thai government's decision to extradite Obrezko was in

accordance with Thailand's domestic law and its obligations

under the related treaties on extradition, "while fully

respecting the due process of law of the defendant."

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.