Karim Baratov, a Canadian citizen who was born in Kazakhstan, was considered a flight risk by Justice Alan Whitten, who remanded Baratov in custody until May 26.
The United States claims that Baratov worked with Russian intelligence agents who paid him to break into at least 80 email accounts, including those of specific targets with non-Yahoo accounts.
The judge said that Baratov had no reason to stick around as he could continue his wealth-generating activities anywhere in the world.
Baratov faces US charges including conspiracy to commit computer fraud, conspiracy to commit wire fraud and identify theft, and could face decades in a US jail if found guilty on all charges.
His lawyer Amedeo DiCarlo says that it was not him, and he would consider appealing the bail decision if the court is unable to schedule a expeditious extradition hearing.
Federal prosecutor Heather Graham told the court that the attorney general of Canada will be ready to proceed with an extradition hearing by June 12, according to media reports.
The United States last month charged two Russian intelligence agents, Baratov and another alleged hacker over the 2014 theft of 500 million Yahoo accounts, the first time the US government had criminally charged Russian spies for cyber offenses.
The other alleged hacker is Alexsey Belan, one of the FBI’s most-wanted cyber criminals, who was arrested in Europe in June 2013 but escaped to Russia before he could be extradited to the United States, according to the US Justice Department.