A recent breach of the unclassified network for the Pentagon’s Joint Staff was persistent and evolved quickly from a failed attack just a week before, the head of the National Security Agency said Tuesday, offering a window into the barrage of cyberattacks that the U.S. military confronts daily….

His [Admiral Michael Rogers, who heads the NSA and U.S. Cyber Command] description of the breach suggested it was aggressive, persistent and sophisticated, though he wouldn’t identify the group he believes was behind the attack.

Adm. Rogers described a digital battlefield that is active and intense, with a constant stream of cyberattacks from nations and criminal groups, as well as potential threats from the hacking capabilities of terrorist groups.

A big concern for Cyber Command is the interest that foreign countries have in breaking into the U.S. power grid, despite extensive security precautions, he said. Some of the attacks may be attempts to pave the way for more damaging assaults in the future.

“We have seen nation states spending a lot of time and a lot of effort to try to gain access to the power structure within the United States, to other critical infrastructure, and you have to ask yourself why,” Adm. Rogers said. “It’s because in my mind they are doing this with a purpose, doing this as a way to generate options and capabilities for themselves should they decide that they want to potentially do something.”

Image: NSA Director Adm. Mike Rogers, Jan. 31, 2012 (photo: US Navy)