Le Thi Hoang rents a motorcycle taxi at 10:00 pm, knocking on the doors of neighbourhood Internet cafes. The reason - her son Phan Le Hong Duc is not home yet, and the worried mother knows the teenage boy is playing computer games somewhere.
"They all said that there were no children inside but actually I knew there were, because from the outside I could hear the sounds of them playing games," Hoang, 54, recalled.
At 5:00 am, his gaming finished for the night, Duc finally came home.
He was addicted.
His late nights at the keyboard had taken the place of evening classes at school, which he was skipping.
His mother felt he needed help, and she found it at Vietnam's first treatment programme for online game addicts.
Most people in Vietnam remain farmers but against this traditional background is a rapidly modernising nation confronting 21st century problems including computer game addiction.
The government says about one quarter of the 86 million people in Vietnam already have Internet access.
Asia's Internet gaming craze hit the country only about four years ago, but now online game shops can be seen even in rural villages, and the number of gamers is expected to rise.
Late last year a report by US-based Pearl Research, a consultancy specialising in games and interactive entertainment, forecast that Vietnam's online gamers will exceed 10 million by 2011.
"I don't know whether I can call myself an addict of online games," said Nguyen Nam Cuong, 15, playing in a Hanoi Internet shop during his school holidays.
Almost all of the 30 computers were occupied by youngsters engrossed in fighting or football games, the only noise coming from their keyboards.
Cuong said he plays one or two hours on school days and about double that during the holidays.
"I enjoy it. Here, I think I can live a more interesting life than my actual life," says Cuong.
Nguyen Thanh Nhan, director of the centre that runs what he called the country's first cyber addict treatment programme, did not know how many game-players need help.
"I can only say that the figure is very big," he said, noting that "thousands" of people called to ask about the course run by the Communist Youth Union, which also offers other educational programmes for young people.
"Online game addiction is something like drug addiction," says Nhan, 35, director of the Union's Southern Youth Centre.
Duc, 15, admits that he was addicted.
"When I first started, I played from around five to six hours a day and the time played just increased day by day. Sometimes the longest I played was 10 hours overnight," he said in an interview arranged by the Youth Union.
He said he favoured a game in which teams of four or five players fight each other. With 20,000 dong (1.11 US) in daily breakfast allowance from his mother, Duc said he had enough money to play for at least five hours at Internet cafes.
"No, I did not eat anything," he said.
Betting on the games also helped to fund his addiction.
"Mostly, our team won," said Duc, who failed grade eight because of his gaming.
Duc's symptoms were "not that serious" compared with others who stole, quit school or turned to violence because of their habit, Nhan said.
Duc's mother, a professor at a teachers' college, said her son eventually realised he had a problem. Unlike others, he did not have to be pushed into treatment, she said, adding the 16-day course was worth the fee of about 3.5 million dong.
"We are ready to pay to take back our children," she said.
Duc was one of 20 teenagers in the first course, run on weekends, last November.
Nhan said the organisers studied successful programmes from China and South Korea but came up with their own method which incorporates a type of group therapy, "so they can share with each other about their feelings."
The course also aims to re-establish bonds between the addicts and their families through simple activities like baking a cake or having a barbecue, he said.
"They told us about what are the precious things in life," said Duc.
A second course, which ended in early June, treated about twice as many addicts and incorporated physical training because many game players are very weak, Nhan said.
Five psychologists were among the more than 30 staff treating the addicts on Duc's course, he said.
Among their goals was to expose the youngsters to new activities and ways of expressing themselves.
"Suddenly, they discover that they like football or they like hip hop dancing," Nhan said.
About 90 percent of participants give up online gaming, and those who continue to play are more respectful of their families, he said.
While the government has, in years past, tried to control excessive computer gaming with regulations, Nhan said such efforts will not work.
"We must change the awareness, the behaviour of the children themselves," he said.
The bespectacled Duc says he now dreams of being a pop singer. He already looks the part, with a hairstyle reminiscent of a Japanese manga comic character, a black and white shirt, and a dragon pattern on his trouser leg.
The treatment programme sparked his interest in hip hop, he says, and insists on demonstrating his skills even though there is no music.
Duc twists his body, arms moving slowly, feet sliding. Then he falls to the floor, gets up, and puts his stylised baseball cap on sideways -- a dance of success.