The owner of Ticketmaster has confirmed there was "unauthorised activity" on its database last month.
A group of hackers, known as ShinyHunters, claim to have stolen data belonging to more than 500 million global Ticketmaster customers.
Ticketmaster owner Live Nation confirmed that a "criminal threat actor" offered what it alleged was company user data for sale on the dark web.
Live Nation confirmed it identified "unauthorised activity" on May 20th primarily relating to Ticketmaster.
"[We] launched an investigation with industry-leading forensic investigators to understand what happened," the company said in a filing to the US Securities and Exchange Commission (SEC).
"On May 27th 2024, a criminal threat actor offered what it alleged to be company user data for sale via the dark web.
"We are working to mitigate risk to our users and the company, and have notified and are cooperating with law enforcement.
"As appropriate, we are also notifying regulatory authorities and users with respect to unauthorised access to personal information," it added.
The company said the incident is not likely to have "a material impact" on its overall business operations.
"We continue to evaluate the risks and our remediation efforts are ongoing," it added.
A screenshot of the Ticketmaster website. Photo by: Jack QuannCybersecurity expert Ronan Murphy told The Pat Kenny Show the hack shows 'someone was asleep at the wheel'.
"To get that volume of data off a network literally would take days," he said.
"So these guys were in there and they were moving these vast quantities of data over an internet connection and nobody caught them.
"That is a huge misstep by them, it will be very difficult to defend and they're going to have a lot of explaining to do," he added.
It comes as US authorities are seeking to break up Ticketmaster's 'monopoly' across the live concert industry.
Earlier month the country's Justice Department filed a civil antitrust lawsuit "for monopolisation and other unlawful conduct that thwarts competition in markets across the live entertainment industry".
It says the lawsuit seeks to restore competition in the live concert industry and provide better choices at lower prices for fans.
