A new mobile phone Trojan has appeared affecting the Symbian 60 operating system.

Dubbed Fontal.A it has to be downloaded by the phone's owner for infection, but once installed the phone is damaged and prevented from rebooting. It is just the latest example of malicious code, including worms and viruses, that target mobile devices.

Fontal.A was discovered on Wednesday and is transferred to mobile phones as an SIS format installer file called "Kill Saddam By OID500.sis".

Mobile phone users who are infected with Fontal should not turn off their phone before removing the Trojan, said anti-virus company F-Secure. The company has posted instructions for removing the Trojan.

Unlike earlier threats to mobile devices, such as the Cabir worm, Fontal does not attempt to spread from phone to phone. Phone users could only be infected by downloading the SIS file containing the Trojan from a website or peer-to-peer file-sharing network.

Malicious programs that run on mobile platforms, such as Symbian, have become more common since Cabir, the first mobile worm, was identified in August 2004. Variants of Cabir have since spread to 16 countries. In March, anti-virus companies also identified the first mobile phone worm, CommWarrior, that spreads using MMS.