An Garda Síochána is warning the public of Invoice Redirect Fraud and CEO Fraud, and that there has been a "noticeable increase" in this type of crime in recent weeks.

It says everyone should treat any request to change bank account details with extreme caution.

It adds that criminals have succeeded in defrauding companies for very substantial amounts of money.

One firm lost over €200,000, while another lost almost US$500,000 (€453,594).

But Gardaí say many people and businesses have lost smaller amounts of money.

Criminals send e-mails to businesses or individuals purporting to be one of their legitimate suppliers.

These e-mails contain a request to change the bank account details that the business has for a legitimate supplier, to bank accounts controlled by the criminals.

These requests can also come by letter or phone call - so Gardaí say caution should be attached to any such request.

The criminal intention is that when the legitimate supplier next sends an invoice to the company seeking payment, the victim business acts on the new banking instructions and sends the payment to the criminal's bank account.

In many instances, the business does not know it is a victim of this crime until the legitimate supplier sends a reminder invoice for payment.

A businessman who was recently the victim of this type of scam has issued advice to others:

• Trust no e-mail full stop: Incoming and outgoing mails can be blocked or redirected without you being aware. Assume all e-mails incoming and outgoing in your company are always being read by fraudsters for extended periods of time
• Check all incoming e-mail addresses that they are correct and coming from a trusted source - it is important also to check other e-mails addresses copied on the mail chain, in order to check that they are also genuine
• Change requests are a red letter warning: Be especially vigilant for any requested changes of bank payment details, for example, amounts to be paid, account number, name of bank etc
• Always pick up the phone to your supplier/vendor to verbally confirm the change request details

Detective Chief Superintendent Pat Lordan, of the Garda National Economic Crime Bureau, said: "Victims of Invoice Redirect Fraud range from very small businesses to large companies and the consequences of falling for a scam of this nature can be catastrophic and result in the closure of businesses and redundancies.

"If you are not sure pick up the phone and speak to someone in the invoicing company".