In its third such incident in four years, Marriott International was on the defensive this week in confirming a data breach involving a property near Baltimore-Washington International Airport.

The breach occurred last month and the hotel company claimed the issue was contained within six hours. It said an investigation was underway before a hacker group contacted the hotel to attempt to negotiate a ransom.

The breach first was reported by DataBreaches.net, with which a group claiming to be the threat actors communicated about their infiltration of Marriott’s systems. The group told DataBreaches it had tricked a single employee into giving the hackers their credentials. Through that individual’s computer, the group was able to exfiltrate 20GB of data.