As many as 300 people mostly working in low-paid jobs in Ireland could have been recruited into an extensive money-laundering network linked to West African criminals involved in cybercrime.
The network was busted last week by Garda fraud detectives who raided 15 homes and businesses in several countries and froze 350 bank accounts.
Gardai believe the network had a three-tier structure, with around 10 key figures at the top.
Detectives suspect that the crime gang used a second tier of middlemen to recruit low-paid immigrants working in factories, service industries and labouring jobs to open the bank accounts here for money-laundering purposes.
They suspect that potentially up to 300 people were recruited in this way, often by middlemen targeting their places of work, demonstrating the potentially huge scale of the operation.
Gardai observed large sums of money, in some cases €20,000 or more, lodged to these bank accounts, and later transferred on, minus a small percentage of a suspected payment for the account holder.
The value of the fraud has been put at €15m but Gardai say this is a conservative estimate, given the scale of the money-laundering network they uncovered last week.
Investigators are focusing on the 10-strong gang, which is comprised of families and close associates, most of them Nigerian, and living in Ireland for some time.
According to Garda sources, the suspects have comfortable lifestyles, although without any obvious means of income. Some are claiming social welfare.
Gardai believe that around €15m suspected of being laundered by the gang is the proceeds of cyber frauds perpetrated in Ireland but mostly abroad, particularly involving 'invoice redirection fraud'. This entails tricking a person or company into transferring funds to a particular bank account, by sending bogus emails purporting to be a supplier notifying of a new bank account.
Once transferred, the funds are laundered through a series of bank accounts, including accounts in Ireland, before being transferred out of the country again, in a variety of ways, including buying high value products here and exporting them.
Gardai believe the Irish-based suspects are part of an international network of West Africans engaged in invoice redirect fraud globally. Some of the stolen funds that washed through Irish accounts had moved through bank accounts in China and west Africa.
In addition to the 300-plus bank accounts in Ireland, the Garda's National Economic Crime Bureau (GNECB) identified a further 170 bank accounts abroad.
The GNECB seized computers, phones, ledgers, log books, bank statements in raids on 15 homes and business premises last week. Also confiscated were four SUVs and a false passport. Arrests are expected to follow.
Superintendent Alf Martin, who is leading the investigation, said a team of detectives worked over many months tracing connections between dozens of suspect bank accounts.
He said that last week's raids produced new evidence that confirms what the Gardai had already established, and provides further insight into who was transacting, how and what methods they were using.
"Money laundering is probably one of the more serious crimes that can be committed because without it, front-line crime is almost irrelevant. As regulations freeze the use of cash in all societies in the developed world, criminals have to forge greater ties with money launderers to ensure they are able to disguise the source of the funds," he said.
The National Economic Crime Bureau has been working to raise awareness of cyber crimes and ransom attacks amongst businesses in Ireland in recent years.
Some of the large organisations targeted by fraudsters here include Dublin Zoo and Meath Education and Training Board, from which around €750,000 was stolen.