An American-led military invasion of Afghanistan took just months to uproot al-Qaida from the rocky slopes of Tora Bora and the White Mountains.

But nearly four years later, even the combined might of the United States and its allies have had a far more difficult time scouring the Internet for the shadowy network of Islamic fundamentalists. The British government's announcement in July that it planned to clamp down on people who run Web sites that incite terrorism has had no noticeable results to date.

"For al-Qaida, the survival of the ideology is a lot more important than the survival of any of their physical assets or members, and the Internet is a way to ensure the propagation of that ideology," said Rebecca Givner-Forbes, an analyst for the Terrorism Research Center, which provides research services to the federal government.

Al-Qaida has adopted online tactics that mirror its offline techniques for evading discovery: reliance on a constantly shifting collection of Internet sites and hostile takeovers of Web servers where propaganda can be posted. Last year, a server operated by the Arkansas highway office was hijacked and used to distribute 70 files including videos featuring Osama bin Laden.

During the past few years, according to terrorism analysts, al-Qaida has embraced the Internet as a new tool for organizing, training and propagandizing. A group believed to be al-Qaida's Web-based propaganda arm recently debuted a weekly state-of-affairs Webcast and is reportedly searching online for recruits to aid with the coverage--meaning that the group will need to find more hijacked computers to distribute the additional content.

What remains unclear is how the U.S. government will respond to the increasing visibility of its far-flung nemesis.

"Obviously, these Web sites, there's more and more of them, and it is a matter of ongoing interest to U.S. intelligence," said an official with the federal government's National Counterterrorism Center, who spoke on condition of anonymity. "They have proliferated...Al-Qaida sees the propaganda value in terms of developing these sites."

That leaves the U.S. government with two obvious choices: attempt to sabotage the Web sites that appear to have the closest ties to al-Qaida's leaders, or monitor them closely to unearth who might be behind their operation. (The National Counterterrorism Center, created by President Bush last year as an offshoot of the CIA, would not comment.)

Most analysts interviewed by CNET believe the federal government has chosen the watch-and-learn approach.

"It is very useful to monitor the content of these sites," Givner-Forbes said. "If you shut down these sites, they would find a way to continue...The community would kind of find a way to continue and would just make it harder for us to access and to eavesdrop on the sites." Some of the Web sites are already protected from the public by usernames and passwords, she said.

If the U.S. government did choose to engage in a limited form of what pundits used to call an "infowar," there may be few legal barriers standing in the way.

Jonathan Zittrain, co-founder of the Berkman Center for Internet and Society at Harvard Law School, said he suspected such a practice could happen legally. Intelligence operatives could classify the deed as a covert operation that would be reported later to Congress, he said.

"If the government chose to conduct an operation overseas to bring

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