An external server held by the Heritage Foundation containing old donor information was hacked, the organization confirmed on Wednesday in response to a report from Politico.

“We experienced a malicious, unauthorized data breach of six-year-old documents on an external server that appear to contain personal information of private donors, who we are notifying. We are unable to verify the authenticity of files circulated online,” Heritage said in a statement. In addition to possibly containing financial information, it contained correspondence between Heritage staff and donors.