We are awaiting more detail from BA but at the moment, it appears to only apply to bookings made or changed and paid for online at ba.com

Quote from the BA website:
“This [data breach] relates to customer bookings made or changed between 22:58 BST August 21 2018
and 21:45 September 5 2018 inclusive.
We will be contacting affected customers directly to advise them of what has happened and are advising
them to contact their banks or credit card providers and follow their recommended advice.”

More details available on the British Airways Home Page