SYDNEY—A cyberattack on one of Australia’s largest telecoms companies could have accessed the personal information of as many as 9.8 million customers, in what one lawmaker called the most significant data breach in recent years.
Optus, an Australian unit of Singapore Telecommunications Ltd., said it doesn’t yet know who was behind the cyberattack that could have exposed customer information dating back to 2017, including names, dates of birth and phone numbers. The company, which said it first became aware of the breach on Wednesday, said some identity documents might also have been compromised.