Hyatt Hotels Corp said on Wednesday that its payment processing system was infected with credit-card-stealing malware in an attack discovered three weeks ago, the latest in a series of breaches at hospitality firms.

Company spokeswoman Stephanie Sheppard said in an email late on Wednesday that the attack was discovered on Nov. 30.

She did not say if the attackers succeeded in stealing payment card numbers, how long its network was infected or how many of the chain's 627 hotels were affected.

"Customers should review their payment-card account statements closely and report any unauthorized charges to their card issuer immediately," she said.

Hyatt, controlled by the billionaire Pritzker family, is the fourth major hotel operator to warn of a breach since October.

Hilton Worldwide Holdings Inc and Starwood Hotels & Resorts Worldwide Inc last month disclosed attacks on payment processing systems. . Donald Trump's luxury hotel chain, Trump Hotel Collection, also confirmed the possibility of a data security incident.

Representatives at a Hyatt call center set up to handle inquiries about the breach said the malware was programmed to collect payment cardholder names, card numbers, expiration dates and internal verification codes.

Hyatt said it had hired third-party cyber security experts to investigate the incident.

"We have taken steps to strengthen the security of our systems," Sheppard said in the email. "Customers can feel confident using payment cards at Hyatt hotels worldwide."

Hyatt did not disclose the type of malware used in the attack.

The company said that customers should look for information on the attack at www.hyatt.com/protectingourcustomers.

Cyber intelligence firm iSight Partners in late November warned merchants about a new strain of payment-card-stealing malware dubbed ModPOS that it said evades almost all security software.

iSight held briefings with dozens of firms, including hospitality companies and retailers, to provide them with information on how to uncover ModPOS infections. – Reuters