Email addresses and other contact information have been stolen from a European Central Bank database following a security breach.
The ECB said the information related to those who had registered to attend its events, such as conferences or visits, and was not encrypted.
However it said other details in the dataset, such as downloads made from its website, were encrypted and no system or market-sensitive information was taken in the attack.
The ECB said the matter first came to its attention after it received an anonymous email seeking money in return for the stolen data.
It said it had contacted German police about the theft and an investigation is under way.
The ECB also said it was in the process of contacting those who may have had their contact information stolen, while all passwords on its website have been changed as a precautionary measure.