EasyJet announced on Tuesday that it has suffered a major cyber attack from a "highly sophisticated" source.
The budget European airline, which has seen its fleet grounded by the coronavirus, told the stock market that the unauthorized access to its systems had been closed off.
An investigation by the airline revealed that approximately 9 million customers had their email addresses and travel details accessed, while 2,208 customers had their credit card details exposed. Affected customers will be contacted in the by May 26, EasyJet said.
The airline first learned of the attack in January, according to the BBC.
The company was not immediately available for comment when contacted by CNBC.
EasyJet CEO Johan Lundgren said in a statement that the company takes the cyber security of its systems seriously, "however, this is an evolving threat as cyber attackers get ever more sophisticated."
Lundgren said EasyJet will be urging affected customers to be "extra vigilant," especially if they receive suspicious emails. The airline said customers should be extra cautious about any communications purporting to come from EasyJet or EasyJet Holidays.
"We will continue to invest in protecting our customers, our systems, and our data," he said. "We would like to apologize to those customers who have been affected by this incident."
EasyJet said it is working with the National Cyber Security Center and the Information Commissioner's Office, which is the U.K. data regulator.
Andrew Tsonchev, director of technology at cybersecurity firm Darktrace, said: "It comes as no surprise that well-known organizations who are very publicly affected by the pandemic — and are known to have furloughed lots of staff — would be the targets of sophisticated cyberattacks, with the potential to cause significant reputational damage."
He added: "Globally across our customer base — we've seen an uptick in highly targeted and sophisticated attacks like these. Access 'downstream' to clients and customer data is often the goal of these attacks, as withholding this data secures not only a quick ransom payout at a time when companies are keen to keep cost down, but can also provide vital nuggets of information to launch secondary attacks."