Concert promoter Live Nation says it is investigating a cyber attack at its Ticketmaster unit, days after experts urged customers to change their passwords.

Hackers are allegedly offering to sell customer data on the dark web.

The US entertainment giant said it had discovered “unauthorised activity” on 20 May in a third-party cloud database that mostly contained Ticketmaster data.

Live Nation added that “a criminal threat actor offered what it alleged to be company user data for…