The details of about 500,000 online bank accounts and credit and debit cards have been stolen by a virus described as "one of the most advanced pieces of crimeware ever created".
The Sinowal trojan has been tracked by RSA, which helps to secure networks in Fortune 500 companies.
RSA said the trojan virus has infected computers all over the planet.
"The effect has been really global with over 2000 domains compromised," said Sean Brady of RSA's security division.
He told the BBC: "This is a serious incident on a very noticeable scale and we have seen an increase in the number of trojans and their variants, particularly in the States and Canada."