According to Qantas, the hackers have targeted one of the airline's customer centers and gained access to a computer system used by a third party.
There, they gained access to sensitive information such as names, email addresses, phone numbers and other personal data of six million customers.
"We continue to investigate how large a proportion of the data has been stolen, but we expect it to be a significant proportion", says Qantas in a statement.
"There has been no impact on Qantas' operations or the airline's security", it says further.
