(CNN) -- The next large-scale military or terrorist attack on the United States, if and when it happens, may not involve airplanes or bombs or even intruders breaching American borders.

Cyberattackers shut down one Georgian government site and defaced another with images of Adolf Hitler.

Instead, such an assault may be carried out in cyberspace by shadowy hackers half a world away. Internet security experts believe that it could be just as devastating to the U.S.'s economy and infrastructure as a deadly bombing.

Experts say last week's attack on the former Soviet Republic of Georgia, in which a Russian military offensive was preceded by an Internet assault that overwhelmed Georgian government Web sites, signals a new kind of cyberwar, one for which the United States is not fully prepared.

"Nobody's come up with a way to prevent this from happening, even here in the U.S.," said Tom Burling, acting chief executive of Tulip Systems, an Atlanta, Georgia, Web-hosting firm that volunteered its Internet servers to protect the nation of Georgia's Web sites from malicious traffic.

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