Credit unions, large multinational banks and regional banks have all been attacked.
According to a joint report by software security firm McAfee and Guardian Analytics, more than 60 firms have suffered from what it has called an "insider level of understanding".
"The fraudsters' objective in these attacks is to siphon large amounts from high balance accounts, hence the name chosen for this research - Operation High Roller," the report said.
"If all of the attempted fraud campaigns were as successful as the Netherlands example we describe in this report, the total attempted fraud could be as high as 2bn euro (£1.6bn)."
The automated malicious software programme was discovered to use servers to process thousands of attempted thefts from both commercial firms and private individuals.
Read more: Sky News
