The breach described by ORNL certainly appears to fit into the classic mold of an APT attack in which attackers first try to compromise systems using highly targeted phishing mails and then drop zero-day malware to snoop on and steal data, Mogull said

But until more details are released it is hard to know for sure, other analysts said.

"The term 'Advanced Persistent Threat' is definitely being and used as an excuse way too often, as in 'Well, it wasn't really our fault it was an Advanced Persistent Threat'," said John Pescatore an analyst at Gartner. "Advanced simply means it got past your defenses and persistent means it took you too long to detect it once it got in."

Pete Lindstrom, an analyst with Spire Security, said the tern APT is often used these days as a face saving measure. "The definition of APT is so sufficiently muddled that anyone can claim APT and be right in some sense and wrong in another," he said. "The proof is in the defenses that could have prevented it -- if they are fundamental security measures then the notion of APT has no meaning."

This is the second time that Oak Ridge has fallen victim to a phishing attack. In 2007, after infecting internal systems via phishing emails.