“The National Office of Cyber Security is engaging with Ticketmaster to understand the incident,” a government spokesman said in a statement.

A well-known hacking group calling itself ShinyHunters posted evidence of the hack on the dark web, according to a screenshot shared widely on social media, claiming to have swiped the personal details of 560 million clients.

The group demanded a ransom payment of US$500,000, describing it as a “one-time sale”, according to the post.

Ticketmaster, a California-based company, operates one of the largest online ticket sales platforms in the world.

The US Department of Justice last week filed a major antitrust lawsuit seeking to break up an alleged monopoly held by Live Nation Entertainment and its Ticketmaster subsidiary in the live music industry.

Ticketmaster’s pricing practices, with high fees and lack of alternatives, have long been a political issue in the US, with little done historically to open up the market to more competition.