Businesses are being warned to be aware of an online scam - known as invoice redirect fraud - which has cost Irish companies thousands of euro and where large and small firms are being targeted on a daily basis.

Criminals send emails to businesses purporting to be one of their legitimate suppliers with the supplier's new bank account details and a request to change the account to one that will ultimately benefit the criminals.

These requests can also come by way of letter or phone call.

Last year, Dublin Zoo paid out €500,000 through false invoicing.

Some of this money was recovered through the quick action of the zoo, but the outstanding amount was spread across 50 different accounts in Europe and has not been retrieved.

Criminal investigations are continuing in the case.

Detective Chief Superintendent Patrick Lordan of the Garda National Economic Crime Bureau said this type of fraud had been going on for some years.

Speaking on RTÉ's Morning Ireland, Det Lordan said it was important for businesses to not take changes to bank account details from companies they deal with on face value as few organisations change their bank and if they do, they do not notify customers through email.

Det Lordan said the fraud was carried out by people both overseas and in Ireland. They use emails that look like the real suppliers' address but with some slight difference.

Often the fraudsters use students' and young people's bank account details by offering them a fee to allow use of their accounts for a few days.

Anyone who allows their account to be used in this way is committing an offence, he said.

If an organisation is notified of any bank changes, Det Lordan advised picking up the phone and talking to someone you know in the company to confirm this directly.

If a company has been targeted by fraudsters, Det Lordan said they should contact gardaí immediately.

"It is important to note that victims of invoice redirect fraud range from very small businesses to large corporations and the consequences of falling for a scam of this nature can be catastrophic and can result in the closure of businesses and redundancies so all employees should receive training in relation to avoiding this type of scam", he warned.