WASHINGTON — The International Monetary Fund, still struggling to find a new leader after the arrest of its managing director last month in New York, was hit recently by what computer experts describe as a large and sophisticated cyberattack whose dimensions are still unknown.

The fund, which manages financial crises around the world and is the repository of highly confidential information about the fiscal condition of many nations, told its staff and its board of directors about the attack on Wednesday. But it did not make a public announcement.

Several senior officials with knowledge of the attack said it was both sophisticated and serious. “This was a very major breach,” said one official, who said that it had occurred over the last several months, even before Dominique Strauss-Kahn, the French politician who ran the fund, was arrested on charges of sexually assaulting a chamber maid in a New York hotel.

Asked about the reports of the computer attack late Friday, a spokesman for the fund, David Hawley, declined to provide details or talk about the scope or nature of the intrusion. “We are investigating an incident, and the fund is fully functional,” he said.