Ticketmaster Ireland has notified customers about a potential breach of security compromising their payment details.
Anyone who bought a ticket from the site between February and June 2018 could be at risk.
In an email to customers this evening, the ticketing website said malicious software was identified on a customer support product hosted by Inbenta Technologies, an external third-party supplier to Ticketmaster.
It said: "As soon as we discovered the malicious software, we disabled the Inbenta product across all Ticketmaster websites."
Ticketmaster said because of Inbenta's product running on Ticketmaster websites, some of customers' personal or payment information may have been accessed by an unknown third-party.
Ticketmaster is recommending that customers monitor account statements for evidence of fraud or identity theft.
The company said forensic teams and security experts are working around the clock to understand how the data was compromised.