In 2001, months after George W. Bush became the 43rd president of the United States, Liu became a leading member of a voluntary Chinese hacker army that was involved in one of the largest and most public cyberbattles between Chinese and US hackers.

At the time, internet-savvy Chinese youths, most still in high school and university, were angry over China's frequent diplomatic friction with the United States and Japan. They had agitated for months for some action.

Some launched individual hacking attacks against US and Japanese targets, Liu said. They then boasted of their acts and shared technical tips on leading social media platforms, chat rooms and online bulletin boards known as BBS.

But the real cyberwar did not start until early April 2001, when a US spy plane and a Chinese fighter jet collided over the South China Sea. Liu said that after the incident, hundreds of Chinese websites suffered attacks believed to have originated from the United States. A student of computer science and budding hacker at the time, Liu started discussing organised counterstrike plans with his friends in chat rooms. "We were so angry and decided to fight back," he said.

Liu, who had in 2000 joined a loose hacker group and later registered the name China Honker Union, rallied his troops and joined other hacker groups and independent hackers in a counterstrike. The term "honker", which means "red hacker" in Chinese, indicates patriotism and a lack of self-interest, Liu said.

During the Labour Day holidays starting on May 1, the self-organised young Chinese hackers started a week-long cyberwar on US websites. In one of their biggest successes, Liu said, he and his friends created a huge amount of data traffic and forced the White House website to shut down for two hours. He insisted that all the actions were done voluntarily by the hackers, and they received no government encouragement or support.

"It felt superb," said Liu. "We were so excited, taking shifts and working 24/7 [to keep up the attacks]."

It was considered a landmark event for Chinese hackers and a highlight for the China Honker Union. The group attracted more than 80,000 members in the following months, making it the largest known hacker organisation to date in China's internet history.

The Sino-US hacker war of 2001 also established the modus operandi of China's "patriotic hackers" of the early years, Liu said. Inspired by the aggressive, often nationalistic rhetoric of mainstream media against perceived foreign offences and threats, the young hackers continued to organise via chat rooms and BBS, and launched attacks on the websites of foreign governments, businesses and sometimes media outlets.

"We were united by the patriotic impulse. We believed we were defending ourselves on the principle that the Chinese wouldn't be bullied," Liu said. "This is the spirit of Chinese honkers."

However, the spirit began to fade after the cyberwar. In the next few years, disagreements among key members of the honker union led to a bitter split and the eventual disintegration of the group.

In 2002, Liu and some friends discovered a security loophole on the website of a big domestic airline and informed their webmaster how to repair it. To their surprise, airline officials contacted them and asked for a meeting. Liu saw an opportunity to turn their prankish hobbies, which often involved illegal online activities, into a gainful career.

"At the time some government officials also contacted us and told us not to organise any more cyberattacks on foreign websites," Liu said, though he declined to give further details.

"We needed to make a decision," he said. "Above all, most of us who were students had to find practical things to do after our graduation."

With a few friends from the honker union, Liu started an internet company and they gradually distanced themselves from active hacking activities. His hacker experience and his technical know-how, however, remain defining factors for his business. Although his first start-up company failed within months, Liu, unfazed, continued on the road of internet entrepreneurship.

He published a book, , about hacking technology and internet security, and used the proceeds to build another company, Shanghai Xianxin Technology.

It develops IT application software mainly for commercial use, such as firewalls and test and scanning tools, and it also offers online training courses on hacking and internet security.

As the original registrar of the China Honker Union, Liu also kept the trademark for his new ventures, a move that angered and alienated many of his former comrades. On the last day of 2004, the founder of the union, a young computer expert who went by the pseudonym "Lion", announced in an online open letter that the union would officially disband.

To this day, few people know Lion's real identity. Liu declined to discuss the former comrade.

While Liu has been busy in the past decade applying his hacking skills to profitable internet entrepreneurship, other veterans of the Sino-US cyberwar have tried to remain true to the hacker spirit.

Eagle Wan, a leader of another hacker group that participated in organised attacks on US websites in 2001, later founded the Intelligence Defence Friends Laboratory, or IDF Lab, to promote research and education into internet security technology.

"Patriotism or online crimes have all betrayed the spirit of geeks," said Cooper Pei, a protégé of Wan's and a current team leader at the lab.

Now 25, Pei was too young to have participated in the 2001 cyberwar, but he said he joined the lab because he was fascinated by the hackers' obsession with attaining technological supremacy in attacks and defence online.

The lab's founder, Wan, now has a day job as a Beijing-based senior executive at a multinational technology firm. He declined to speak to the for this story.

Pei says the IDF lab is one of a few organisations in China that promotes the "true spirit of geeks", a term they prefer to use instead of hackers.

"Overall, bigger hacker organisations mostly go commercial, while smaller groups get involved in online crimes," he said.

The lab began offline training in 2010 on online security. It also provides trend reports and analysis on hacking technology, groups and major conferences.

"Online courses are one of the major ways to train young geeks," said Pei.

"You don't need a certificate or a degree. As long as you are eager to learn online security knowledge, you can find a suitable group and join them."

The individual hackers' pursuit of profit and personal gain has contributed to the decline of large, amateur hacker groups in China, said Professor Liu Deliang, director of the Asia-Pacific Institute for Cyberlaw Studies. Today's hackers turn increasingly to profitable online crimes such as banking fraud or identity theft, and Beijing doesn't have strong and comprehensive laws to effectively stop these crimes, he said.

"I've been urging the related departments to build a public safety network to stop hackers and organised crime from invading, stealing and selling personal information for profit," Liu Deliang said.

Almost half of mainland internet users have encountered at least one Trojan virus attack, and one-fifth of them have experienced account or password theft, according to a 2010 report by the China Internet Network Information Centre.

"Besides the domestic online crime concern, China might encounter a cyberwar, for example, with the United States," he said. "We have a lot work to do."

However, cyberwars and hacker conflicts are none of Liu Qing's concern. He is focusing on his new mobile game business. "Mobile games will be the biggest piece of cake in the IT industry, much more profitable than the online security business," he said. "I'm up for a new game."