British Airways
British Airways' new Airbus A380 arrives at a hanger after landing at Heathrow airport in London, July 4, 2013. REUTERS/Paul Hacket

Over 380,000 British Airways customers' financial data were stolen in recent weeks, the airline said Thursday. Bookings made on the airline's website between Aug. 21 and Sept. 5 were affected by the theft.

In a statement issued late Thursday, the chief executive of British Airways apologized for the "sophisticated, malicious criminal attack" on the firm's security systems.

"We are deeply sorry for the disruption that this criminal activity has caused. We take the protection of our customers' data very seriously," Alex Cruz told the BBC. "At the moment, our number one purpose is contacting those customers that made those transactions to make sure they contact their credit card bank providers so they can follow their instructions on how to manage that breach of data."

Cruz said the breach was first discovered Wednesday evening by British Airways' network of partners that monitor websites around the world. A partner alerted the airline, which began investigating overnight to get details of the cyberattack.

"The moment that actual customer data had been compromised, that's when we began immediate communication to our customers," he added.

Under General Data Protection Regulation rules, companies must inform regulators within 72 hours of becoming aware of a data breach.

"If the breach is likely to result in a high risk of adversely affecting individuals’ rights and freedoms, you must also inform those individuals without undue delay," according to guidelines from the Information Commissioner’s Office (ICO), the independent regulator that upholds information rights in Britain.

The National Crime Agency and National Cyber Security Centre told BBC they were assessing the incident involving British Airways.

Meanwhile, the airline issued a statement giving out details of some frequently asked questions during such an incident.

Shares in British Airways parent IAG fell by 2.3 percent as of Friday morning in London.

This is not the first customer relations problem to affect the airline in recent times.

In July, British Airways apologized after IT issues caused dozens of flights in and out of London's Heathrow Airport to be canceled.

"An issue with a supplier IT system was resolved overnight. We are doing everything we can to keep any knock-on disruption to our services to a minimum," the airline said in a statement at the time. "We have apologized to our customers for the delay to their travel plans."

In May 2017, serious issues with the airline's IT systems led to the cancelation of all flights from Heathrow and Gatwick. More than 75,000 customers were stranded at Europe's busiest airport over a holiday weekend.