"At this point, we have no reason to believe that any personal information was sought for fraud purposes," the message to employees said.
Lockheed Martin Corp, the Pentagon's No 1 supplier by sales and the biggest information technology provider to the US government, disclosed two weeks ago that it had thwarted a "significant" cyber attack. It said it had become a "frequent target of adversaries around the world."
Also hit recently have been Citigroup Inc, Sony Corp and Google Inc.
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.