According to local press reports, the gang worked alongside three Russian hackers who provided them with usernames and passwords that had been stolen using spyware.

The Russian hackers are thought to have distributed passwords for thousands of Turkish Internet users in exchange for a 10% cut of the money stolen.

A 20-strong team from the Izmir Organised Crime Bureau began investigating the case after hundreds of Internet users complained about unexpected withdrawals from their online bank accounts in January.

The team traced the IP addresses of the computers making the illegal transactions, and this week made simultaneous raids at addresses in Izmir, Fethiye, Didim and Kusadasi in Turkey.

Commenting on the case, Graham Cluley, senior technology consultant at anti-virus technology vendor Sophos, says: "The Turkish authorities should be applauded for looking into this case so speedily, but this is just the tip of the iceberg.

"Phishing and spyware is a global problem, and all computer users need to defend themselves better against these kind of menaces if they want to continue to bank online safely."

Sophos says its research shows that Russia is one of the top producers of malware, accounting for 4.1% of all malware authored during the last year.