Personal data belonging to staff, members and suppliers of the Royal Dublin Society was compromised during a cyber attack last week.
The RDS said it became aware it was the victim of a ransomware attack on 8 February, during which data was extracted from servers, before it was encrypted to make it inaccessible to the RDS.
In a statement today, the RDS said immediate steps were taken to restore the systems, reinforce existing security and mitigate the potential impact.
Correspondence from the RDS to its members, seen by RTÉ News, stated that data stolen includes names, addresses, phone numbers and email addresses.
It said that in a "small number of cases, bank details may have been compromised in respect of those who paid their membership fee by direct debit".
The RDS said in this letter that it will contact people whose bank details may have been accessed "when the situation becomes clearer".
It recommended that all members contact their bank as a precaution.
The letter warned that criminals may sell this data or use it for further scams or fraudulent activity.
In a statement, the RDS said it had engaged the services of a specialist cyber security firm and the matter has been reported to An Garda Síochána and the Office of the Data Protection Commissioner.
The RDS said the ransomware attack has had no impact on its commercial operations.
It said it deeply regrets that this occurred and urged people affected who have further queries to contact them.