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.

Instead, such an assault may be carried out in cyberspace by shadowy hackers half a world away. And 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. 'The U.S. is probably more Internet-dependent than any place in the world. So to that extent, we're more vulnerable than any place in the world to this kind of attack,' Burling added. 'So much of what we're doing [in the United States] is out there on the Internet, and all of that can be taken down at once.'....