Peter Levashov from Saint Petersburg, a 37-year-old who goes by a string of names, was arrested at Barcelona airport on April 7th by Spanish authorities acting on a US warrant.
US prosecutors accuse the purported hacker of controlling the Kelihos network of tens of thousands of infected computers, stealing personal data and renting the network out to others to send spam emails by the millions and extort ransoms.
His defence team had argued that the US extradition demand was "politically motivated".
Levashov, a computer specialist, had served in the Russian army and worked for President Vladimir Putin's United Russia party, according to his lawyers.
In the course of his work he had access to confidential documents which he fears authorities in the US may demand he turn over to them if he is extradited there, the lawyers had argued.
But the High Court said in its ruling that "none of the allegations relating to the political motivation" for the extradition request "has been accepted".
Levachov has three days to appeal the court's decision. A US federal grand jury in April slapped Levachov with an eight-count indictment. The charges include fraud, identity theft and conspiracy.
Levashov could allegedly order remotely the delivery of fraudulent spam and malicious computer viruses on behalf of whoever would pay him to do so.
US officials claim he was proud of his work and advertised the ever-improving effectiveness of his spam services with a standard price list. For legal ads, he charged $200 per million spam emails. For illegal scams and phishing attacks, it was $500 (€425) per million.
To help someone with a stock manipulation, he allegedly wanted a deposit of $5,000-$10,000 (€4,250-€8,500) to share his list of 25 million traders. He also demanded five percent of the gains made on the stock.
During any 24-hour period, prosecutors say the botnet generated and distributed more than 2,500 unsolicited spam emails that advertised various criminal schemes.
Levashov has not been tied to Russian interference in last year's US presidential election.
But his operation depended on sending spam emails that allowed hackers to penetrate the computers of the Democratic Party to steal data. That was exactly the kind of botnet service he allegedly sold to criminals.