"British Airways has become aware of some unauthorised activity in relation to a small number of frequent flyer executive club accounts. This appears to have been the result of a third party using information obtained elsewhere on the internet," an airline's message read.
The airline apologized to its customers and emphasized that the hackers did not get access to passengers' names, bank details, flight history and other personal information.
The affected accounts have been frozen by the British Airways till it solves the issue, according to the messages sent to its customers.
It is not known yet who is behind the hacking, though it was reportedly carried out by an automated computer program.