The International Monetary Fund's computer system was targeted by hackers, believed to be connected to a foreign government, who retrieved e-mails and other documents, according to a person familiar with the attack.

The incident occurred before former Managing Director Dominique Strauss-Kahn was arrested for sexual assault on May 14, according to the person, a security expert who couldn't be identified because he wasn't authorized to speak on the subject. He didn't say which government is thought to be behind the intrusion, which he said involved the removal of a "large quantity" of data.

The infiltration follows reported hacks at Google Inc., Sony Corp., Lockheed Martin Corp. and Citigroup Inc. in the past three months. The FBI has said it would increase efforts to combat cyber-attacks by criminal gangs, industrial spies and foreign governments. On June 10, Spanish police arrested three suspected members of the online hacking group Anonymous, which has said it carried out attacks on governments and websites belonging to Sony and MasterCard Inc.