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NATO is looking into claims that hackers have breached its security and accessed scads of material so confidential the hacker group itself deemed it "irresponsible" to publish them all, despite a series of international raids Tuesday designed to corral the hacking activity.

"NATO is aware that hacker group released what it claims to be NATO classified documents on the internet," a NATO spokseman said in a statement. "NATO security experts are investigating these claims. We strongly condemn any leak of classified documents which could potentially endanger the security of NATO allies, armed forces and citizens."

The group, which goes by the name "Anonymous," claimed to be sitting on about 1 gigabyte of data. The hackers broadcast a link to a PDF file Thursday via Twitter, showing what appeared to be a document headed "NATO Restricted."

The group's actions have become intolerable, Steven Chabinsky, deputy assistant FBI director, said in an interview with NPR.

"We want to send a message that chaos on the Internet is unacceptable," Chabinsky said. "[Even if] hackers can be believed to have social causes, it's entirely unacceptable to break into websites and commit unlawful acts."

The group followed up with a statement to the FBI and Chabinsky, with a list of things it deems unacceptable: "Governments lying to their citizens and inducing fear and terror to keep them in control ... corporations aiding and conspiring with said governments ... lobby conglomerates who only follow their agenda to push the profits higher."

The group claimed that a second link it tweeted later linked to a second restricted NATO document on "outsourcing CIS in Kosovo (2008)."

Sixteen suspected members of "Anonymous" were arrested Tuesday in states across the country, from California to New York, in a federal raid on the notorious hacking group.

Anonymous is a loosely organized group of hackers sympathetic to WikiLeaks. It has claimed responsibility for attacks against corporate and government websites worldwide.

The group also claims credit for disrupting the websites of Visa and MasterCard in December, when the credit card companies stopped processing donations to WikiLeaks and its founder, Julian Assange.

The group's message was clear: In spite of the string of recent arrests, the "hactivism" will continue.

"We are not scared any more. Your threats to arrest us are meaningless to us as you cannot arrest an idea."