Almost 400,000 customers who booked a flight between 22:58 BST August 21 2018 and 21:45 BST September 5 2018 were affected. The airline detected the breach when a third party noticed some unusual activity and informed us about it. We immediately acted to close down the issue, and started an investigation as a matter of urgency British Airways announced the incident has been resolved and all activity resumed, customers can check in and make bookings. Relevant authorities have been informed and an investigation is ongoing.”]
Source: https://www.bitdefender.com/blog/hotforsecurity/british-airways-hacked-400000-customers-affected/