The International Monetary Fund (IMF) said it was the victim of a "sophisticated" cyber attack earlier this year.
The bank which doles out funds to indebted nations so long as they agree to go capitalist said the hack installed a "digital insider presence", according to a report in the News York Times.
A spokesman for the bank said the incident was being investigates and claimed the ogranisations servers were secure.
The New York Times report said IMF staff were informed of the attack Wednesday but if failed to make a public announcement until the email to staff was leaked.
The e-mail alluded to "suspicious file transfers" and said a PC at the Fund had been "compromised and used to access some Fund systems".
The attack too place before the IMF's former managing director Dominique Strauss-Kahn was arrested for sexual assault on May 14, but the Fund has not given a precise date fro when the hack took place.
Bloomberg said it had information to suggest a "foreign government" had something to do with the hack and that a “large quantity” of data had been extracted, but the news service failed to give details of who its source was, beyond its usual "person familiar with the matter" and it seems not have have second-sourced this information either.