A Russian hacker extradited by Georgia to the U.S. admitted Monday that he executed the largest known cyber-attack against a U.S. bank, pleading guilty to charges that he stole data on more than 80 million clients of JPMorgan Chase & Co. and other institutions that netted hundreds of millions of dollars in ill-gotten gains, as reported by Bloomberg.

The hacker, Andrei Tyurin, 36, was accused of stealing customer information from 12 financial news companies, banks and other financial firms, including Fidelity Investments, E-Trade Financial and Dow Jones & Co. His co-conspirators used the information to ply customers with spam emails promoting stocks, hoping to cash out at higher prices, the U.S. government said.

Tyurin, who was apprehended last year in the Republic of Georgia and extradited to the U.S., pleaded guilty to charges of conspiracy, wire fraud, illegal online gambling and computer hacking. As part of the deal with prosecutors, the government will recommend that he serve 15 to 20 years behind bars, though the final decision on his sentence will be up to the judge.