Hacking group Anonymous has claimed to have hacked into NATO servers, according to the Blottr.com news service.
Blottr claims it acquired a confidential document when Anonymous hackers announced a download location, which has since stopped working.
Anonymous claimed to have accessed NATO data in a tweet: "Yes, #NATO was breached. And we have lots of restricted material. With some simple injection. In the next days, wait for interesting data :)"
They later said: "We are sitting on about one Gigabyte of data from NATO now, most of which we cannot publish as it would be irresponsible. But Oh NATO...."
They later released the document, obtained by Blottr.
NATO says it is aware of the Anonymous claims and is investigating.
The breach is believed to be part of Anonymous's ongoing AntiSec campaign that has targeted several organisations the group believes are corrupt or failing in their security practices.