NATO is investigating how its computer network was hacked.
A group of international hackers calling itself Anonymous says it breached the alliance's security and downloaded hundreds of confidential documents.
The attack comes days after 21 suspected members of Anonymous were arrested in the United States, Britain and the Netherlands for cyber crimes, including 14 over an online attack on the PayPal website claimed by Anonymous.
An indictment said the attack on PayPal was ''retribution'' because the site terminated a donation account for WikiLeaks.
