Ticketmaster has suffered a cyber attack in which data of up to 40,000 UK customers may have been accessed.
The ticket sales site said that malicious software on third-party customer support product Inbenta Technologies was behind the hack.
In a statement issued on a dedicated website set up after the security breach was identified on Saturday, Ticketmaster said less than 5% of its global customer base had been affected, but not customers in North America.
It added: "As a result of Inbenta's product running on Ticketmaster International websites, some of our customers' personal or payment information may have been accessed by an unknown third party.
"We have contacted customers who may have been affected by the security incident.
"UK customers who purchased, or attempted to purchase, tickets between February and June 23, 2018, may be affected, as well as international customers who purchased, or attempted to purchase, tickets between September 2017 and June 23, 2018."
A spokesman for the National Cyber Security Centre (NCSC) said: "We are aware of a cyber incident affecting Ticketmaster.
"The NCSC is working with our partners to better understand the incident."