Spanish police have arrested a Russian programmer following US allegations of large-scale hacking.
Pyotr Levashov was held in Barcelona on Friday and is remanded in custody.
Spanish police said Mr Levashov controlled a botnet called Kelihos, hacking information and installing malicious software in hundreds of thousands of computers.
The arrest was part of a "complex inquiry carried out in collaboration with the FBI", police said.
Mr Levashov is subject to a US international arrest warrant and a Spanish court will hear whether he can be extradited.
Much of his alleged activity involved ransomware - blocking a computer's access to certain information and demanding a ransom for its release.
Mr Levashov's wife Maria told Russian broadcaster RT that the arrest had been made in connection with allegations that Russians had hacked the US presidential election.
She said Spanish police had told her the arrest was in connection with "a virus which appears to have been created by my husband and is linked to [Donald] Trump's victory".
However, Agence France-Presse news agency quoted a source close to the matter in Washington as saying that Mr Levashov's detention was "not tied to anything involving allegations of Russian interference with the US election".
A US intelligence report released in January alleged that Vladimir Putin had tried to help Mr Trump to victory, allegations strongly denied the Russian president.
Mr Trump later commented that the outcome of the election had not been affected.
Several cybersecurity experts, including Brian Krebs, have also linked Mr Levashov to a Russian spam kingpin, who uses the alias Peter Severa.