BA said on Thursday evening: "British Airways is investigating, as a matter of urgency, the theft of customer data from its website, ba.com and the airline's mobile app".
The airline said the hack hit customers who made bookings from 10.58pm on August 21 until 9.45pm on September 5.
The airline said 380,000 payments were compromised.
The National Crime Agency (NCA) said: "We are aware of reports of a data breach affecting British Airways and are working with partners to assess the best course of action". "We take the protection of our customers' data very seriously".
BA chairman and chief executive, Alex Cruz, said the carrier was "deeply sorry" for the disruption caused by the criminal activity.
Champion Stephens booted from US Open
Sevastova broke the 25-year-old American's serve twice in the opening set, then broke her again to take a 2-0 lead in the second. Next up for the 28-year-old is Serena , who beat Pliskova later in the day to move into the semis.
He said that BA has a network of partners that monitor websites around the world and that one of those partners alerted the airline. The air carrier also recommends affected customers to call their bank and follow their instructions, to minimize potential financial damage.
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. "No passport or travel details were stolen".
Mat Thomas said he placed a booking on 27 August, but had not been contacted about the breach. "Unfortunately, this is likely to be another PR disaster for British Airways, especially as it includes tickets bought in their September sale which is being widely promoted at the moment".
Also of concern is its reliability as a trusted airline.
"I've not heard anything from them on this and I've just had to cancel the card I used. Sadly, this data breach is likely to knock back its efforts".
Michael Capuano (D-MA) conceded to Boston City Councilwoman Ayanna Pressley after polls closed in the state. Pressley defeated Capuano by arguing that it was time for a change in representation in the district.
Maximum sustained winds of the unnamed system have been clocked at 30mph and the system is moving west-northwest at 15mph. If Gordon were to take more of a turn to the north then our forecast could change considerably by Wednesday and Thursday.
Kei Nishikori is headed to the US Open semifinal following a dramatic upset victory over Marin Cilic on Wednesday. Keys said she will look to home support on Thursday when she resumes her rivalry with Osaka.
The White House on Tuesday threatened military intervention if the Syrian government used chemical weapons. If it's a slaughter, the world is going to get very, very angry. "Let's f-king kill him! Let's go in.
Del Potro - the 2009 victor of the men's singles at Flushing Meadows - breezed past Borna Coric in the final match of the day. Serena, seeded 17th, routed Venus 6-1, 6-2 in matching the most-lopsided victory in the Williams sisters' series.
For instance, the electricity went out in an annex on the site, causing some frozen specimens to begin to rot. In 2015, for example, a blaze destroyed the prestigious Museum of the Portuguese Language in Sao Paulo .
A child has been killed in Florida after a tree was blown on top of his mobile home in an incident which may be linked to Gordon. Brandon Drake, a meteorologist for the National Weather Service in Topeka, said theories differ on how the storm will progress.
Bill Clinton described himself as an Aretha Franklin "groupie", saying he had loved her since college. Franklin died August 16 at age 76.
Thai cave boys honoured by Thailand's prime minister
Wisely, Unsworth himself has elected to let Wood do all the talking for him-and to let Musk keep packing the evidence folder. Mr Unsworth's lawyer Mark Kennedy from the firm Howard Kennedy told the BBC that Mr Musk's allegations were baseless.
Quake halts all trains on Japan island
Government spokesman Yoshihide Suga said two people had been killed, with local media reported around 40 were missing. Houses in the town were hit by landslides, and one report said five residents were found with no vital signs.
Dallas Cowboys: Earl Thomas trade still on the table
Thomas' reaction to the lack of a resolution was clear in his post: "The disrespect has been noted and will not be forgotten". Thomas has since reported to the Seahawks, but he still doesn't appear to be thrilled with his situation.
Amazon Hits $1 Trillion Valuation
Amazon has become the second publicly traded company to be worth US$1 trillion (NZ$1.52 trillion), hot on the heels of Apple . Amazon has briefly become the second US-listed firm to have a market value of more than $1 trillion (£779bn).
John Millman Just Knocked Off Roger Federer At The US Open
The 13-times grand slam victor had made easy work of the opening set, breaking Sousa twice, the second time to close out the set. Kei Nishikori , runner-up in 2014, was also pleased to get through in three sets in blazing sunshine on Louis Armstrong Stadium.