Other than being off-line for several hours, the site was undamaged, he said, noting that the Ministry, realizing it could be targeted, had taken security precautions, such as installing a firewall.

Still, the ministry "views with gravity the fact that the site was not accessible to those who wanted to visit," Noy said. "This technique…is an unacceptable act of virtual terrorism."

An Israel Defense Force spokesman said that the army's site showed no evidence of being attacked, despite connection problems stemming from line overload.

NetVision's security experts, tracked the hackers to U.S. and European university servers, but are not certain that the attacks originated there, a statement said.

Retaliation has been swift. Unnamed hackers have broken into the Hezbollah Web site, www.hizballa.org, and replaced its home page with an image of an Israeli flag and an instrumental recording of "Hatikva."