Names and e-mail addresses of people using jobs website recruitireland.com have been compromised.
Tom Crosby, managing director of the site, confirmed that it had suffered a data breach at 2pm yesterday.
He said that the Data Protection Commissioner and the Gardai were notified immediately and are investigating the event.
400,000 e-mails have been affected by the security breach. The information compromised first names, last names and e-mail addresses. CV information was not compromised.
The website has been taken down as a result of the breach.
'We take this incident and any attempted breach of our database extremely seriously and this is being investigated internally by our own people, externally by Brian Honan who is a security expert and by Gardai,' the company said.