The Washington Post reports:

The group calling itself Anonymous claimed credit Thursday for hacking into NATO servers and stealing 1 gigabyte of sensitive information as part of its campaign to harass and humiliate prominent targets.

The group has attempted to post online some documents collected in the incident and vows to post more soon, but it also said it has decided to withhold some others because posting them would be “irresponsible.” NATO did not confirm the group’s account.

“NATO is aware that a hackers group has released what it claims to be NATO classified documents on the Internet,” Damien Arnaud, a spokesman for the trans-Atlantic military alliance, said in an e-mail. “NATO security experts are investigating these claims. We strongly condemn any leak of classified documents, which can potentially endanger the security of NATO allies, armed forces and citizens.”

Groups calling themselves “hacktivists” — which target Web sites and servers in pursuit of political agendas — have joined the list of cyber threats identified by government and corporate security officials.

“It is one of the up-and-coming biggest concerns for the FBI,” said Robert E. Nickel, unit chief in the FBI’s Public Private Alliance Unit, speaking at a cyber conference last week.