A group of hackers say they have stolen the personal details of 560 million Ticketmaster customers.
ShinyHunters, the group claiming responsibility, says the stolen data includes names, addresses, phone numbers and partial credit card details from Ticketmaster users worldwide.
The hacking group is reportedly demanding a $500,000 (£400,000) ransom payment to prevent the data from being sold to other parties.
The Australian government says it is working with Ticketmaster to address the issue. The FBI has also offered to assist, a spokesperson for the US Embassy in Canberra told Agence France-Presse.
A spokesperson for the FBI told the BBC it "has no comment on this matter".
"The Australian Government is aware of a cyber incident impacting Ticketmaster," a spokesperson for the Australia Home Affairs Department said in a statement to the BBC's media partner CBS News.
"The National Office of Cyber Security is engaging with Ticketmaster to understand the incident."
The American website Ticketmaster, one of the largest online ticket sales platforms in the world, has yet to confirm whether it has experienced a security breach.
Cyber security experts are warning that the claims could be false but authorities in Australia, where it was first reported, have confirmed they are investigating.
An advert with some data samples allegedly obtained in the breach have been posted on the website BreachForums - a newly relaunched hacking forum.
ShinyHunters has been linked to a string of high-profile data breaches resulting in millions of dollars in losses to the companies involved.
Hackers allegedly stole personal details of more than half a billion Ticketmaster customers.
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