From approximately 12:30 p.m. PST on Tuesday, the English news portion of the Al Jazeera Web site seemingly dropped off the Internet, said Roopak Patel, senior Internet analyst at Keynote's public services division, who stressed that the reason the site is inaccessible can't be determined.

"There's a whole host of reasons that the site could not be accessible," he said. "The server could be not able to serve up data as fast...or it could be an attack. At this point, we are not able to correlate between the lack of access and the cause."

The Arab satellite TV network launched its English-language Web site on Monday, attracting significant media coverage. The site hosts the station's controversial video coverage, which has included images of U.S. soldiers killed and taken prisoner.

An Al Jazeera representative did not return e-mails seeking comment. A representative of the media company's Web hosting firm, Horizons, was not immediately available to comment.

While the outage may just be the result of the sites becoming an overnight curiosity, several media reports point to a denial-of-service attack by anti-Arab hackers as a potential cause.

However, Keynote's Patel said that there seems to be no external evidence that points definitively to a hack attack. While such an external event could be the cause, he also pointed to traffic loads that swamped the site and too many requests for pages as possibilities.

"We cannot determine whether it is any one of those three issues," he said.

A representative of network performance measurement service Matrix NetSystems said that in general the company hasn't seen signs of serious hacking since the start of the war.

"We were prepared to see malicious worms and viruses launched in conjunction with what's going on in Iraq, but we aren't seeing anything like that," said Tom Ohlsson, a spokesman for the company. "There is no (widespread) disruption of traffic across the Internet."

Ohlsson did stress that the number of minor attacks and defacements on Web sites has risen in recent days.

Online vandals have defaced a greater number of Web sites following the start of the war, according to defacement tracker Zone-H.org. Attackers who tag Web sites with digital graffiti normally want the world to know and so immediately notify sites like Zone-H.org of the defacement. The Web site will immediately make a copy of the Web site and keep the copy as evidence of the defacement.

On an average workday, 350 sites are defaced, said SyS64738, the administrator for Zone-H.org. On the weekend, as many as 1,000 sites can be defaced, he said.

After the U.S. strikes began on Iraq, those numbers climbed significantly. Now Zone-H.org is seeing as many as 2,500 site defaced every day by both pro-American vandals and pro-Arab vandals.

Some virus writers have attempted to use interest in the war to spread their programs among unsuspecting PC users.