An Armenian national who was extradited from Ukraine to the United States last year pleaded guilty to participating in a series of attacks in 2019 and 2020 involving Ryuk ransomware, the Justice Department said Thursday.

Karen Serobovich Vardanyan pleaded guilty to computer fraud and conspiracy to commit fraud and extortion. He agreed to pay nearly $1.2 million million in restitution and faces up to 15 years in jail.

The 34-year-old admitted to participating in cybercrime from November 2019 to April 2020 when he and his co-conspirators deployed Ryuk ransomware against three U.S.-based organizations while living in Ukraine and Russia.

Vardanyan’s victims include a Michigan-based company that paid a ransom of nearly $1.2 million in January 2020, a Watsonville, Oregon-based technology company that was attacked in December 2019 and a Texas-based school breached in February 2020.

Prosecutors previously accused Vardanyan and his co-conspirators — Ukrainian nationals Oleg Nikolayevich Lyulyava and Andrii Leonydovich Prykhodchenko, and Armenian national Levon Georgiyovych Avetisyan — of illegally accessing computer networks to deploy Ryuk ransomware on hundreds of compromised servers and workstations between March 2019 and September 2020.

Ryuk ransomware was prevalent in 2019 and 2020, infecting thousands of victims globally across the private sector, state and local municipalities, local school districts and critical infrastructure, including a wave of attacks on U.S. hospitals.

Victims of Ryuk ransomware attacks include Hollywood Presbyterian Medical Center, Universal Health Services, Electronic Warfare Associates, a North Carolina water utility and multiple U.S. newspapers.

Ryuk ransomware operators extorted victim companies by demanding ransom payments in Bitcoin in exchange for decryption keys. Justice Department officials said Vardanyan and his co-conspirators received about 1,160 bitcoins — valued at more than $15 million at the time — in ransom payments from victim companies.

Vardanyan, as part of his guilty plea, also acknowledged that his conviction will have immigration consequences resulting in removal from the United States after serving his sentence. 

The U.S. District Court for the District of Oregon has yet to schedule his sentencing.