The Finnish company posted details of the Trojan horse, which they've named Fontal.A, on Wednesday. Fontal.A affects Nokia Series 60 handsets running the Symbian operating system. The advisory did not say whether any infections had been reported.
Other Trojan horses, or applications that appear to be legitimate but perform illicit activity when they are run, have found their way into smart phones. But unlike the CommWarrior Trojan, Fontal.A does not propagate over Bluetooth wireless networking connections or Multimedia Message Service, which is a mobile technology for sending text messages that can also include images, audio or video. Instead, it is distributed via file-sharing or IRC (Internet relay chat).
Fontal.A tries to install a corrupted file, called "Kill Saddam By OID500.sis," into the infected device, causing it to fail at the next reboot, F-Secure said. If the handset is rebooted, it gets stuck and can't be used until it is disinfected.
The Trojan also damages the application manager, preventing new programs from being installed and stopping the Trojan itself from being uninstalled. The only fix is to reformat the phone. However, doing this causes all data on the handset to be lost, F-Secure said.
The company suggested that the way to avoid Fontal.A and other Trojans is to download files only from known or trusted sources.