Ticketmaster's revealed it was subject to a potential data breach on Saturday June 23rd.
The company says it identified malicious software on a customer support product hosted by Inbenta Technologies - an external third-party supplier to Ticketmaster.
It says "less than 5%" of its global customer base was affected but that "some" customers' personal or payment information may have been accessed.
"As soon as we discovered the malicious software, we disabled the Inbenta product across all Ticketmaster websites", the company adds.
We have created a dedicated website about the recent data security incident, please go to https://t.co/6rVEEO8iTm
— Ticketmaster Ireland (@TicketmasterIre) June 27, 2018
The company says it has contacted all potentially impacted customers who purchased, or attempted to purchase, tickets between February and June, 23rd.
It says it has also contacted all potentially impacted international customers who purchased, or attempted to purchase, tickets between September 2017 and June 23rd, 2018 "out of an abundance of caution".
All notified customers should reset their passwords.
It says forensic teams and security experts are working to understand how the data was compromised.
A special website has also been set up to answer questions about the incident.