A communications and IT vendor for almost all of the world’s airlines, SITA, has been breached in a highly sophisticated attack that compromised passenger data stored on the company’s servers. The airline service provider stored information regarding frequent flyer data across many different characters. The affected servers are in Atlanta and belong to the SITA Passenger Service System, according to a company spokeswoman.

The service operates the systems that process airline passenger data. Malaysia Air and Singapore Airlines have already alerted their customers of the attack and that their passengers’ data may have been compromised. Singapore Airlines alone reported more than 580,000 impacted customers, meaning that the breach could ultimately affect millions of customers spanning across tens of airlines.