After a cyberattack on Christie's auction house earlier this month, a hacker group called RansomHub claimed responsibility.
In a post on the dark web Monday, RansomHub said that it had gained access to the personal information of the firm's wealthy clients and published what it claimed was a "sample" with a few names, nationalities and birth dates.
The group posted the information along with a countdown clock, suggesting they would publish the entire trove in early June.
The group's claims and the authenticity of the data it published could not be immediately verified. But a Christie's spokesperson acknowledged that some client information was taken.
"Our investigations determined there was unauthorized access by a third party to parts of Christie's network," wrote the spokesperson in a statement on Monday. "They also determined that the group behind the incident took some limited amount of personal data relating to some of our clients. There is no evidence that any financial or transactional records were compromised."
The attack, which led to the auction house taking down its site on May 9, came days before Christie's began its all-important 20th and 21st century May auctions in New York. This briefly threw the success of the auctions in doubt.