The International Monetary Fund has been hit by a cyber attack on its computer systems, an IMF spokesman said on Saturday, highlighting a growing rash of network break-ins at high-profile institutions.

The fund is fully functional, said IMF spokesman David Hawley. I can confirm that we are investigating an incident. I am not in a position to elaborate further on the extent of the cybersecurity incident.

Bloomberg News reported the IMF's computer system was attacked by hackers believed to be connected to a foreign government, resulting in the loss of e-mails and other documents.

The attack occurred before the May 14 arrest of former IMF Managing Director Dominique Strauss-Kahn on sexual assault charges, Bloomberg said. It did not identify a suspect government. Cybersecurity experts say it is very difficult to trace a sophisticated cyber break-in to its ultimate source.

An official with the World Bank, the IMF's sister institution in Washington, said the World Bank had cut its network connection with the IMF out of caution. The information shared on that link was non sensitive info, the official added.

The World Bank Group, like any other large organization, is increasingly aware of potential threats to the security of our information system and we are constantly working to improve our defenses, said World Bank spokesman Rich Mills.

The IMF, which has sensitive information on the economies of many nations, was hit during the last several months by what computer experts described as a large and sophisticated cyber attack, The New York Times reported.

The newspaper said the IMF's board of directors was told on Wednesday about the attack.

Experts say cyber threats are increasing worldwide. CIA Director Leon Panetta told the U.S. Congress this week the United States faces the real possibility of a crippling cyber attack.

The next Pearl Harbor that we confront, he said, could be a cyber attack that cripples our power systems, our grid, our security systems, our financial systems, our governmental systems.

This is a real possibility in today's world, Panetta told his June 9 confirmation hearing in his bid to become the next U.S. defense secretary.

ATTACKS ON THE RISE

Internal IMF memos had warned employees to be on their guard.

Last week we detected some suspicious file transfers, and the subsequent investigation established that a Fund desktop computer had been compromised and used to access some Fund systems, said a June 8 email to employees from Chief Information Officer Jonathan Palmer.

Details of the email were first reported by Bloomberg. Reuters' sources confirmed the wording of the email.

At this point, we have no reason to believe that any personal information was sought for fraud purposes, the message to employees said.

The incident comes when attacks on computer systems are said by experts to be on the rise -- notably those targeting major companies and potentially compromising government security and customer information.

For instance, Lockheed Martin Corp, the Pentagon's No. 1 supplier by sales and the biggest information technology provider to the U.S. government, disclosed two weeks ago that it had thwarted a significant cyberattack and said it was a frequent target of adversaries around the world.

Also hit recently have been Citigroup Inc, Sony Corp and Google.

The attack on Lockheed followed the compromise of SecurID electronic keys issued by EMC's Ltd RSA Security division.

SecurIDs are widely used electronic keys to computer systems, designed to thwart hackers by requiring two passcodes: one that is fixed and another that is automatically generated every few seconds by the security system.

SecurIDs are used at the World Bank for remote log-ins.

As an extra precaution, employees receive an automatic email each time they log in from outside, to flag the operation in case it was originated fraudulently by someone else, a World Bank staff member said.

The IMF is seeking a new head following the resignation of Strauss-Kahn after he was charged with the sexual assault of a New York hotel maid.

(Reporting by Lisa Shumaker, Leslie Wroughton, Jim Wolf; Editing by Peter Cooney and Todd Eastham)