It was Sunday shortly after 2 a.m. in the ancient Chinese capital of Luoyang, and Dong Ruiyong had just painstakingly restored the city government's Web site after a crippling day-long hacker attack. Then the electronic intruder came back for more.

"Suddenly, we saw that [the site] was changed again, and then we saw his address, and it was from Taiwan," said Dong, an exasperated local telecommunications official. "It's not as if they were on the mainland, where if they did this kind of damage people could deal with them."

Web sites like Luoyang's have become high-tech battlefields in a new kind of conflict between China and Taiwan. Taiwan's supporters and its opponents on the mainland are plastering dueling slogans on dozens of Web sites on opposite sides of the Taiwan Strait, or shutting the sites down altogether.

The battle was sparked in July when Taiwan's president, Lee Teng-hui, called for Taiwan and China to be treated as equal states. The move infuriated China's leaders, who view Taiwan as a renegade province. Now, the hackers are at war. Taiwan's National Security Bureau reported that mainland hackers have broken into Taiwanese computer networks 165 times since August. Beijing has not released statistics but has acknowledged hacker strikes.

Although the blows are delivered through cyberspace, the trail of wrecked Web pages and crashed computers is causing immeasurable losses--in time, money and data. It also has alarmed security specialists in both places by pointing out their vulnerability.

In some ways, both sides are stealing a page from the future. U.S. and other military officers predict that attacks on enemy computer systems could become an important part of warfare in the coming decades. The threat of cyberattacks has prompted Washington to take new measures to protect U.S. military computers and create a Pentagon unit to penetrate enemy networks in time of war.

While the extent of government involvement in the China-Taiwan attacks is unknown, the Taiwanese and Chinese armed forces have prepared openly for such a conflict. Taiwan's defense minister, Tang Fei, announced earlier this year that his ministry was forming an "information warfare" committee to deal with the threat from China. In July, China's Liberation Army Daily said the country needs to "go all out to develop high-quality 'Internet warriors.' "

"That should include development in exclusive universities, as well as attracting some private computer aces to take part in Internet combat," the paper said. A follow-up article warned of breaches in Chinese computer security: "The wolf has already come. Pick up your hunting rifle!"

The Chernobyl virus, written by a Taiwanese computer engineering student, damaged 360,000 computers in China last April and caused $120 million in damage, according to the official New China News Agency. Taiwanese hackers have warned in online forums that they are planning an attack on Chinese computers on Oct. 1 as a 50th birthday present for the Communist Party.

The keyboard combat across the 100-mile-wide Taiwan Strait began in earnest Aug. 8. A hacker using a computer that is part of China's Jilin Province Information Port broke into the Web site of Taiwan's inspector general and left a message: "Only one China exists and only one China is needed. . . . The Taiwanese government headed by Lee Teng-hui cannot deny it!"

Another hacker using a computer in China planted an image of the five-star Communist Chinese flag on the site of Taiwan's National Assembly and crashed a mainframe computer, according to police investigators in Taiwan. Hackers using computers in Taiwan responded by changing the text on a Chinese State Tax Authority Web site to say "China should stop playing with fire. We will declare independence should you dare to attack us."

Hackers also penetrated the site of China's Security Regulatory Commission twice, and in bold red letters wrote that Taiwan is "divisibly" part of China, a play on Beijing's mantra that the island is "indivisibly" part of the motherland.

Hackers using a computer at a Taiwan university also replaced China's Ministry of Railways site with the text of Taiwan's national anthem and a button that plays the music. The public security bureau in the city of Dongdan also was hit.

In a coup for Chinese hackers, computers run by Taiwan's Bureau of Investigations, an intelligence agency, were successfully attacked on Aug. 15, the bureau announced.

Rare reports about the hacker battle in China's state-run press assert that China has deflected most of the attacks. At one point last month, the Chinese Central Television Web site was attacked by Taiwanese hackers every three minutes, but they never broke through, according to a report in Guangzhou's Yangcheng Evening News.

Computer security experts in China acknowledge that China lags behind its Taiwanese rivals.

Despite China's 1.3 billion population, its Internet users number just 4 million--the same as in Taiwan.

"Taiwan's hackers are extremely skilled because Taiwan got on the Internet earlier," said Xu Rongsheng, a professor at the Chinese Academy of Sciences who advises government officials on Internet security.

Xu, who earlier this year launched a network security software company called NetPower, sees the latest conflict with Taiwanese hackers as a business opportunity.

"I'm paying very close attention to this. I take note of which sites have been hacked, and turned to black or invaded, and then I give them a call and ask them if they need our service," he said.