The airline said the personal and financial details of customers who made bookings on its website or app from 10.58pm on August 21 until 9.45pm on September 5 had been compromised.
Another BA customer, Stephanie Jowers, said she contacted the airline hours before the hack was announced to query a suspicious charge on her account but was not informed it could have been compromised.
The airline said that the breach involved customer bookings made between August 21 and September 5.
The company says its website is working properly now.
A spokesperson added: "We have notified the police and relevant authorities".
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The US has signed similar pacts with less than 30 other countries, the report added, citing a senior US defence official. India already has bought US Apache attack helicopters and other gear, and is negotiating to buy armed drones.
Chief executive Alex Cruz says the company is "100% committed" to compensating customers who have had financial information stolen.
All affected customers had been contacted on Thursday night.
After the computer system failure in May 2017, BA said it would take steps to ensure such an incident never happened again, but in July it was forced to cancel and delay flights out of the same airport due to problems with a supplier's IT systems. This month's data breach has not affected scheduled flights.
Shares in BA's parent, International Airlines Group, were down 2 percent in afternoon trading on Friday.
Enough information was stolen to allow criminals to use credit or bank card information, Mr Cruz said.
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Will I have to get a new card?
"Called bank and had to cancel both mine and my wife's card".
If the breach affects individuals' rights and freedoms, they should also receive a notification without delay. Typically, we're lucky to get a date range of less than six months to a year, which makes a potential victim's response to any threat hard.
BA's website has a page with further information on the breach here, where it confirms that "Every customer affected will be fully reimbursed and we will pay for a credit checking service".
The Guardian reports that 380,000 "payment cards" were affected.
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