Japan Airlines (JAL) has discovered that a cyber-attack may have led to the theft of up to 750,000 customer details from its computer systems.

The carrier said that “approximately 110,000 pieces of customer data may have been compromised,” although this number could increase to 750,000 if the outbound data was sent in a compressed format. The data pertains to JAL Mileage Bank members.

JAL has found no indication that passwords or credit card numbers were stolen as a result of the computer security breach. However, the data could have included mileage membership numbers, enrollment dates, names, dates of birth, workplaces, email addresses, and home and work addresses and phone numbers.

The airline said it has taken steps to block further unauthorized access to its database and has launched a full investigation.