As many as 1,500 computers in the Defense Department were taken off line because of a cyber attack, Pentagon officials said.

Defense Secretary Robert Gates says he expects systems will recover soon after Wednesday's attack.

Gates said the Pentagon sees hundreds of attacks a day, and this one had no adverse impact on department operations. Employees whose computers were affected could still use their handheld BlackBerries.

The attack comes several days after several government agencies within the Department of Homeland Security admitted staffers had been attacked more than 800 times in the past two years.

Click here to read more.

During a press briefing Gates said of the Pentagon cyber attacks: "We obviously have redundant systems in place. ... There will be some administrative disruptions and personal inconveniences."

He said the Pentagon shut the computers down when a penetration of the system was detected, and the cause is still being investigated.

When asked if his own e-mail account was affected, Gates said: "I don't do e-mail. I'm a very low-tech person."

Navy Lt. Cmdr. Chito Peppler, a Pentagon spokesman, said Defense Department systems are probed every day by a wide variety of attacks.

"The nature of the threat is large and diverse, and includes recreational hackers, self-styled cyber-vigilantes, various groups with nationalistic or ideological agendas, transnational actors and nation-states," Peppler said.

The Associated Press contributed to this report.

• Click here to visit FOXNews.com's Cybersecurity Center.