The National Hi-Tech Crime Unit has arrested 12 eastern European nationals who are suspected of laundering funds obtained from the victims through "phishing" e-mails that trick users into revealing their bank account details.
The 12, from Estonia, Latvia, Lithuania, Russia and the Ukraine, were arrested at addresses in London and Kent, where computers, passports, cheque books and bank cards, money and crack cocaine were seized.
Fraudsters using phishing scams are generally based outside the UK and, because they are unable to transfer money directly out of their victims' online account overseas, they need UK intermediaries.
The suspects were recruited by people close to organised crime syndicates in eastern Europe and opened bank accounts into which the stolen money was placed. It was then transferred minus a "commission", to Russia.
Detective superintendent Mick Deats, the deputy head of the NHTCU, said, "Organised crime is targeting internet users, and specifically Russian speakers, in the UK to launder money stolen from online bank accounts where people have been duped into handing over their account details.
"We believe this gang has sent hundreds of thousands of pounds back to Russia. They have targeted a large number of high-street and internet banks and, because they are unable to break into the banks' systems themselves, they are resorting to duping account holders into parting with their details.