"Hacking is a very addictive hobby, or past time, whatever, you want to call it," Mr. Cheng said.

In the case featuring the first jailed Hong Kong hacker, the offender's lawyer said that the teenager suffered asthma and a skin disease, which had isolated him from his classmates, resulting in increasing low esteem. He became a computer hacker to find "satisfaction and achievement", the lawyer said.

Hackers vary in age, but most Hong Kong hacking cases do involve teens, according to the senior superintendent of the Crime Prevention Unit, Computer Crime Bureau.

Whether against hackers, crackers or determined cyber terrorists, the police need to arm themselves with new investigative skills and the best technology, most experts say.

"In a crime scene, we look for dead body, and find evidence from something physical. Now, we refer to analyzing the computer system," said Paul Jackson, senior Superintendent of Crime Prevention Unit.

This unit was formed in 1995, with two staff to manage all computer crime prevention activities, such as giving lectures to computer companies and schools.

"A large percentage of computer crime is committed by adolescents, age 16 to 21, sometimes 13 and 14," said Mr. Jackson. "Some kids think it's challenging to break into a computer's system. They have respect on hackers. I would try to twist it to reality and say something like, 'Would you respect shoplifters?' In fact, it's very common in Hong Kong to hack into an e-mail account. Kids think it's clever."

When facing kids, Mr. Jackson frequently faces master users of software who are already good at hacking techniques. But Mr. Jackson tries to reach their heart.

"One of the students asks me, 'What happens if I hack into a company and asked the boss to give me the job? I can help you to protect your system.' I would say, 'They won't give you a job if you have broken the law and hacked into their system. Why should they trust a person with a criminal mind?'"

Mr. Jackson has allowed some adolescents to personallt demonstrate their hacking skills for him.

"I asked the kid to demonstrate for me, using two computers next to each other. It is done in a controlled environment, with my permission."

He has kept in contact with a few he considers experts. "When a good kid is willing to talk to me, why discourage him? I say to them: 'In the future, you can become a computer security professional if you channel your effort into the right direction.'"

The Crime Prevention Bureau has made visits to more than 20 organizations, including schools, during the first four months of this year; only 23 visits were made in all of last year, reflecting increasing demand for Internet prevention measures.

In recent talks, Jackson reminded company bosses to be aware of the staff they sacked.

"Many hackers come from within companies. One problem is the disgruntled employees. When they get fired, they may take revenge. We recommend to companies that when you fire an employee, don't give them notice and immediately cancel their computer access."