By Bill Hayton
BBC News, Hanoi
Tough new restrictions intended to curb the playing of online computer games have come fully into force in Vietnam.
Online gaming has become a huge industry in Vietnam
They follow concerns from officials and teachers about the effect the games were having on young people playing for many hours at a time.
But some games companies are finding it difficult to implement the new rules.
Some have been slow to introduce the rules and have been fined or closed down. Others, however, continue to flout the law.
Almost every city centre street in Vietnam has an internet cafe.
Most of their customers are young men playing online football or fighting games.
The most popular - Vo Lam or Swordsman - is thought to have a quarter of a million players.
Based on a game developed in China, its use of traditional stories has become very popular.
Some of its players have become virtual addicts, according to one man in a games cafe, Thue.
"Some special cases play this game 24 hours a day - 24 hours a day."
Vietnam's authorities have become concerned about a generation hunched over computer terminals living in fantasy worlds instead of studying, building socialism or even playing football.
In June, they announced new restrictions intended to limit playing sessions to five hours.
Online gaming has become a huge industry in Vietnam and some international games developers have also set up facilities in the country to take advantage of its cheap and talented programmers.
The authorities are happy to see high-tech industries develop, but not to the extent that they might - in their eyes - corrupt the country's youth.