WASHINGTON/LONDON - A major cyber attack on the IMF aimed to steal sensitive insider information, a cyber security expert said on Sunday, as the race to lead the body which oversees global financial system heated up.

The US Federal Bureau of Investigation is helping to investigate the attack on the International Monetary Fund, the latest in a rash of cyber break-ins that have targeted high-profile companies and institutions.

"The IMF attack was clearly designed to infiltrate the IMF with the intention of gaining sensitive 'insider privileged information'," cyber security specialist Mohan Koo, who is also Managing Director, Dtex Systems (UK), told Reuters in London.

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A June 8 internal memo from Chief Information Officer Jonathan Palmer told staff the Fund had detected suspicious file transfers and that an investigation had shown a desktop computer "had been compromised and used to access some Fund systems".

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

The New York Times cited computer experts as saying the IMF's board of directors was told of the attack on Wednesday, though the assault had lasted several months.

The IMF says its remains "fully functional" but has declined to comment on the extent of the attack or the nature of the intruders' goal.

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Jeff Moss, a self-described computer hacker and member of the Department of Homeland Security Advisory Committee, said he believed the attack was conducted on behalf of a nation-state looking to either steal sensitive information about key IMF strategies or embarrass the organization to undermine its clout.

He said it could inspire attacks on other large institutions. "If they can't catch them, I'm afraid it might embolden others to try," said Moss, who is chief security officer for ICANN.

Tom Kellerman, a cybersecurity expert who has worked for both the IMF and the World Bank, said the intruders had aimed to install software that would give a nation state a "digital insider presence" on the IMF network.

That could yield a trove of non-public economic data used by the Fund to promote exchange rate stability, support balanced international trade and provide resources to remedy members' balance-of-payments crises.

"It was a targeted attack," said Kellerman, who serves on the board of a group known as the International Cyber Security Protection Alliance.

The code used in the IMF incident was developed specifically for the attack on the institution, said Kellerman, formerly responsible for cyber-intelligence within the World Bank's treasury team and now chief technology officer at AirPatrol, a cyber consultancy.