The individual is alleged to be the head of the organised crime gang that ran the Carbanak and Cobalt malware campaigns that targeted banks.

Europol said the group had been active since 2013 and infiltrated more than 100 banks in that time.

Cash was siphoned off via bank transfers or dispensed automatically through cash machines.

Luxury goods

The arrest was a "significant success" against a top cyber-crime group, Steven Wilson, head of Europol's Cyber-Crime Centre (EC3), which co-ordinated the long-running, cross-border investigation into the group. said in a statement.

"The arrest of the key figure in this crime group illustrates that cyber-criminals can no longer hide behind perceived international anonymity," he said.

The cyber-thieves got their malware on to bank networks by sending key staff booby-trapped phishing emails, said Europol. The gang used three separate generations of malware, each one more sophisticated than the last, to penetrate and then lurk on financial networks.

Once the machines of key staff were compromised, the gang used their remote access to banking networks to steal money in several different ways.

• cash machines were ordered to remotely dispense money at specific times - letting mules and other gang members scoop up the notes
• inter-bank money transfer systems were instructed to move cash into criminal accounts
• databases were altered to increase account balances. Mules then removed the money via cash machines

Money was laundered via crypto-currencies and payment cards, which were used to buy luxury goods including cars and houses.

Europol, the FBI, cyber-security firms and polices forces in Spain, Romania, Belarus and Taiwan all collaborated to track down the gang, said the European policing agency.