The International Monetary Fund says it was targeted by a sophisticated cyber attack earlier this year.
The New York Times reports that IMF officials say the attack was a very major breach of its systems.
Cyber security officials say the hack was designed to install software to create a digital insider presence.
The IMF says its operations are fully functional. The agency holds sensitive economic data about many countries.
The attack took place over several months.
The New York Times said IMF staff were told of the intrusion on Wednesday by e-mail.
The BBC reports the incident is the latest in a string of high profile cyber security breaches.
In April, the Sony Playstation network was shut down after hackers stole the personal data of about 100 million accounts.
US defence firm Lockheed Martin said in May that it had come under a significant cyber-attack.