3G mobile phone users in Vietnam are vulnerable to attacks by hackers, experts from the Hanoi-based Bach Khoa Internet Security warn. Nguyen Minh Duc, its director, said: "Because all 3G devices are directly connected to each other and open, security risks are very high. "Moreover, all phone operating systems have holes. A hacker can use any internet connection to attack 3G users. "All 3G devices are [also] connected to the provider's server like a local network. Risks for 3G networks are similar to the risks faced by local networks." Bui Quang Minh, a Bach Khoa executive, demonstrated possible attacks by hackers o­n 3G devices, explaining the main risks come from IP addresses, file sharing services, weak passwords, and holes in software. Hackers can take control of users' device or computer to steal information or cause over-billing by sending packages since charges are based o­n upload and download quantity. Other possible troubles include fake SMSs and other risks from viruses and malicious software and distributed denial of service, or DdoS, attacks. Minh recommended that users should o­nly turn o­n 3G networks when they are in need, use a strong password and firewall, configure file-sharing folders, install anti-virus software, and get software updates. They should always be aware of risks and alert to attacks to minimise damage, he said. But Duc said since providers play an important part in protecting customers, if they structure their networks properly and have a firewall to prevent overbilling attacks, it will significantly reduce damage from attacks. Vietnam has four 3G providers – Vinaphone, Mobifone, Viettel, and EVN Telecom – and millions of subscribers.