Another Trojan has been found that targets the Symbian mobile phone operating system.

Affecting Series 60 smart phones, the Trojan can cause complete data loss if not removed within an hour, security experts have warned.

Several owners of Symbian-based handsets have caught the Trojan Doomboot.A. after downloading unauthorised mobile phone games containing the malware, said Anton Von Troyer, marketing manager of anti-virus vendor F-Secure Corp.

F-Secure has warned users on its website that Doomboot.A was in the wild. Von Troyer estimated that around 30 million phones are potentially threatened. But what makes Doomboot.A a serious threat, according to Von Troyer, is the Commwarrior.B worm it contains.

The worm propagates itself by sending messages via MMS and short-range Bluetooth, both of which are fairly standard features in smart phones. "The worm sends a continuous stream of MMS messages, which will drain the battery of most phones in about an hour," Von Troyer said. "When users try to reboot, they can't. Their handsets needs to be reformatted, resulting in complete loss of their data, such as photos, calendar and address book."

Most users wouldn't notice if their phones had been infected, according to Von Troyer. No icons appear - the only indication is a rapid drain of the battery. Users who detect the Trojan have about an hour to open the application manager program in their phone and remove the malware before the battery drains.

"We're suggesting that people use common sense when going to websites and downloading unauthorised Symbian-based mobile phone games," Von Troyer said. "And we're also recommending that they use anti-virus programs to protect their devices from viruses, Trojan horses and worms."