Three men have been held in Dublin overnight by Gardaí as part of an international fraud investigation.
It involves criminals posing as a legitimate company who are owed money.
Senior Gardaí say the arrest of the men, all in their twenties, is "extremely significant".
Two of the men are suspected of tricking a Spanish company into transferring large amounts of money to an Irish bank account.
The third man is thought to have been behind a similar fraud involving an Irish firm.
Gardaí say what is known as an 'Invoice Re-Direction Fraud' involves fraudsters posing as a legitimate company who are owed money.
Most of the money has been recovered.
The suspects are being held at Garda stations in Lucan and the Bridewell.