Australian airline Qantas says a data hack on Monday exposed the personal information of six million customers and it expects the amount stolen to be “significant.”

Qantas has sent emails to customers affected or potentially affected by a cyber attack, but none of its executives have yet fronted the media.

The hack of the Australian carrier follows recent incidents at Hawaiian Airlines and Canada’s WestJet. Here’s what you need to know. Qantas said on Wednesday it is contacting customers after a cyberattack targeted a third-party customer service platform that stored the personal data of 6 million customers.