British Airways today announced the theft of customer data from its website and mobile application.
Consumer advice website MoneySavingExpert says customers who were swept up in the data breach should first seek advice from their bank, then monitor bank and credit card statements closely for signs of possible fraudulent activity.
BA says the breach relates to bookings made between 10.58pm on August 21 and 9.45pm on September 5.
Both the British Airways app and website were hit by the breach.
Cruz said the carrier was "deeply sorry" for the disruption caused by the sophisticated crime, which was unprecedented in the more than 20 years that BA had operated online.
BA could also face a class-action lawsuit from customers if it has failed to protect their data, according to the data privacy lawyer Nick McAleenan of JMW Solicitors.
Anxious customers rushed to social media and helplines after the airline urged anyone who suspected they may have been affected to contact their bank or credit card provider.
Investors were understandably concerned by the news, and shares in IAG sold off sharply at the market open on Friday.
Furious British Airways customers have been left having to cancel their credit cards with many reporting they had money taken from their accounts and rogue direct debits set up in their names.
Hundreds of thousands of British Airways customers have had their financial and personal data stolen after a major hack. It immediately contacted customers when the extent of the breach became clear.
"We will compensate them for any financial hardship that they may have suffered", he told the BBC.
BA, however, was quick to issue a video of Cruz apologizing to customers for the inconvenience and reassuring them that the firm was working "tirelessly" to resolve the issue as soon as possible.
Will I have to get a new card?
Spokespeople for British Airways declined to comment beyond their official statements. BA has said that its encryption was not breached but that the hackers used other "very sophisticated" methods.
"Called bank and had to cancel both mine and my wife's card".