The Luas operator Transdev says an incident which brought down the tram system's website was "a professional attack".

A message on Thursday morning claimed the company had been warned about 'serious security holes' some time ago, but failed to respond.

It also claimed it was being held to ransom for one bitcoin - worth around €3,400.

The website has since been taken offline as investigations continue.

Screenshot: Luas.ie

The company says: "The site is being analysed to identify how the attack occurred and technicians are working to restore the service for the customer."

It says no financial information has been compromised in the attack.

However it has identified 3,226 user records which may have been compromised.

These are records of people signed up to a Luas Newsletter.

The company will write to these people within the next 24 hours, informing them of the potential breach.

Luas has also been in contact with the Data Protection Commissioner.

It says there is no estimation as to the full damage done to the site.

While a date or time for a full restoration of the site is unknown.

"Luas technicians are working on a temporary site for customer information which will be up and running ASAP", it says.

Additional reporting: Jack Quann