Authorities have warned major mobile phone service providers like VinaPhone, MobiFone and Viettel over their loose management of message switchboards.

This has led to customers being swamped with spam messages and advertisements for several services like downloading ring tones, fortune telling, gambling and even "sexual consultancy".

Many customers have lost money responding to messages said that they'd won prizes.

In a recent case, the Hanoi-based EMOBI JSC was found to have sent 800 messages each hour with content related to fortune telling and gambling.

The Ha Trung Communications JSC used prepaid sim cards to send messages to mobile phone users, receiving 58,000 replies that cost customers around 877 million VND (43,000 USD), according to the Sai Gon Giai Phong (Liberated Sai Gon).

Mobile service providers have themselves sent warning messages to their customers about attempts to cheat them.

However the number of switchboards has soared to around 1000 as digital content companies look to take advantage of the lucrative returns they get from offering these "services".

Service providers do not have much of an incentive in curtailing the actions of digital content firms because they earn 60 to 70 percent of the revenues generated by customers' responses.

Officials of the Ministry of Public Security tasked with fighting hi-tech crime say mobile phone service providers are responsible for the situation because they focus on profit and ignore other even illegal content that is sent to customers.

They said service providers should also be held responsible for the chaotic situation in managing prepaid sim cards.

The Ministry of Information and Telecommunications has already asked the providers to collect information from prepaid users, but this has had little effect so far. Currently, people can easily buy prepaid sims without registering their names./.