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Cathay Pacific, one of the major international airliners out of Hong Kong, has suffered a data breach affecting millions.

The airliner announced the breach on Wednesday, noting that hackers had access to a system containing passenger data on 9.4 million people. Cathay Pacific said it first noticed suspicious activity in March, and confirmed that intruders had accessed its network in early May.

It's unclear why it took nearly six months to notify the public. Cathay Pacific didn't immediately respond to a request for comment.

"We are very sorry for any concern this data security event may cause our passengers," Cathay Pacific CEO Rupert Hogg said in a statement.

The data stolen from Cathay Pacific includes passengers' names, nationalities, dates of birth, phone numbers, emails, addresses, passport numbers and historical travel information. The airliner noted that no passwords were stolen. A small number of credit card numbers were also stolen, it said.

Also stolen in the breach were 403 expired credit card numbers and 27 active credit card numbers, the airliner said.

The company said it's reaching out to every person potentially affected by the breach. It'll be providing ID monitoring services from Experian, a credit-monitoring company that had its own data security problems reported in 2013.

Cathay Pacific said it's working with Hong Kong police on the investigation, as well as a cybersecurity firm.

Companies across industries are falling victim to breaches, as hackers seek out vulnerabilities to steal financial data and personal information. They've targeted hotels, restaurants and retailers, with attackers stealing data on millions of unsuspecting patrons.

Cathay Pacific isn't the only airliner on the tarmac to get hit with a hack. In September, British Airways suffered a breach affecting about 380,000 credit card payments.

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