During the last two weeks, the Pentagon's unclassified computer networks have been subjected to "fairly heavy cyber attacks," the military's No. 2 civilian official said Wednesday.

"It was the most organized and systematic attack the Pentagon has seen to date," said John Hamre, deputy secretary of defense.Hamre told reporters at a breakfast meeting that the event had "all the appearances of a game" and apparently was perpetrated by "a small number of individuals."

He said he was constrained from divulging too many details about the attacks because the military was working in cooperation with the Justice Department in pursuing potential criminal activity.

The attacks did not appear to be connected with the ongoing crisis involving Iraq, he said. They appear to be directed at unclassified information, such as personnel records or payroll matters.

"Our classified networks were intact and not penetrated," he said.

"During the last two weeks, the department experienced fairly heavy cyber attacks," Hamre said. He said the apparent hackers attempted to enter networks handled by all the military service branches.

"All the services had penetration to some degree," he said.