Hyatt Hotels has revealed that its payment system has been compromised, as credit-card stealing malware was discovered in the system about three weeks ago, according to Reuters. A company spokesperson sad in an email that the attack was discovered on Nov. 30 but did not say if any credit card numbers were stolen.

"Customers should review their payment-card account statements closely and report any unauthorized charges to their card issuer immediately," spokesperson Stephanie Sheppard wrote.

The Chicago-based company has 627 properties but said that only 318 were affected by the attack, BBC News reported.

Officials at the Hyatt call center said that the malware was designed to collect payment cardholder names, card numbers, expiration dates and verification codes.

However, Sheppard indicated that the company has fixed the problem. "We have taken steps to strengthen the security of our systems. Customers can feel confident using payment cards at Hyatt hotels worldwide," she said, adding that a forensic investigation was underway, according to The Wall Street Journal.

Hyatt customers concerned that their cards might have been compromised have been advised to log on to www.hyatt.com/protectingourcustomers. The company has not offered any kind of identity protection service, which some companies offer when there has been a security breach, according to PC Magazine. 

Hyatt is the fourth hotel company to warn its customers of a breach in the last few months, Reuters noted. Hilton Worldwide Holdings and Starwood Hotels & Resorts Worldwide also reported attacks on their payment processing system. The Trump Hotel Collection also said that it might have experienced a data security problem.