Telstra, the largest telecoms operator in Australia, has revealed it suffered a data breach. Telstra does not reveal its cyber security vendors.

Its main rival Optus faced a massive cyberattack two weeks ago. Optus is yet to reveal compensation for the victims of the cyber security incident.

Telstra has 18.8 million customer accounts equivalent to three-quarters of Australia’s population. Telstra said an intrusion of a third-party organization exposed some employee data dating back to 2017. Telstra did not reveal additional details about the cyber security issue.

According to local media, a Telstra internal staff email put the number of affected current and former employees at 30,000.

The data that was taken was very basic in nature, limited to names and email addresses, a company spokesperson said in a statement.

“We believe it’s been made available in an attempt to profit from the Optus breach,” the spokesperson also said without elaborating.

Telstra did not comment on the number of people affected or when the breach occurred, but said it affected current and former staff only.

Australia’s telecommunications, financial and government sectors have been on high alert since Optus disclosed on Sept. 22 that a breach of its systems that may have compromised up to 10 million people’s accounts. The data exposed included home addresses, drivers’ licenses and passport numbers.

Optus owner Singapore Telecommunications has said it is assessing the potential cost of the attack, while law firms contemplate class action suits.